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的关联查询，数据库表除了前面小节中已经定义好的用户表...","2026-09-12T08:29:57.518395Z",[87],[],{"permalink":412,"excerpt":407,"lastModifyTime":413,"phase":116},"\u002Farchives\u002Fmybaitsplus-join-query","2026-09-13T05:25:32.424638Z",[415],{"metadata":416,"spec":417,"status":418,"postCount":96},{"name":87,"creationTimestamp":88},{"displayName":90,"slug":87,"cover":91,"description":92,"priority":27,"hideFromList":93,"preventParentPostCascadeQuery":93},{"permalink":95,"postCount":96,"visiblePostCount":96},{"metadata":420,"spec":423,"status":432,"categories":436},{"name":421,"creationTimestamp":422},"post-mybaitsplus-enum-value-745dbc08","2026-09-12T08:29:56.730649Z",{"title":424,"slug":425,"cover":426,"excerpt":427,"publishTime":429,"categories":430,"tags":431,"priority":27,"pinned":93,"deleted":93,"visible":111,"allowComment":112},"Mybatis Plus 通用枚举（图文讲解）","mybaitsplus-enum-value","\u002Fupload\u002F167359425246371-MHdo.jpg",{"raw":428,"autoGenerate":93},"\r\n大家好，本小节中，我们将讲解 Mybatis Plus 通用枚举的用法。那么，什么是通用枚举呢？之前小节中，我们的用户表有个性别字段 gender，在插入数据时，我们的示例代码大致如下...","2026-09-12T08:29:56.787230Z",[87],[],{"permalink":433,"excerpt":434,"lastModifyTime":435,"phase":116},"\u002Farchives\u002Fmybaitsplus-enum-value","本小节中，我们将讲解 Mybatis Plus 通用枚举的用法。那么，什么是通用枚举呢？之前小节中，我们的用户表有个性别字段 gender，在插入数据时，我们的示例代码大致如下...","2026-09-13T05:25:33.487169Z",[437],{"metadata":438,"spec":439,"status":440,"postCount":96},{"name":87,"creationTimestamp":88},{"displayName":90,"slug":87,"cover":91,"description":92,"priority":27,"hideFromList":93,"preventParentPostCascadeQuery":93},{"permalink":95,"postCount":96,"visiblePostCount":96},{"metadata":442,"spec":445,"status":454,"categories":458},{"name":443,"creationTimestamp":444},"post-mybaitsplus-common-annotation-80f197dc","2026-09-12T08:29:56.056296Z",{"title":446,"slug":447,"cover":448,"excerpt":449,"publishTime":451,"categories":452,"tags":453,"priority":27,"pinned":93,"deleted":93,"visible":111,"allowComment":112},"Mybatis Plus 常用注解（超详细）","mybaitsplus-common-annotation","\u002Fupload\u002F167334634342163-ZyfL.jpg",{"raw":450,"autoGenerate":93},"大家好，本文主要带大家来看下 Mybatis Plus 框架中，使用频率非常高的几个注解及其属性值，因为编写此本教程目的是为了大家快速入门并使用 Mybatis Plus，关于注解更高级的用法请参考官网...","2026-09-12T08:29:56.114067Z",[87],[],{"permalink":455,"excerpt":456,"lastModifyTime":457,"phase":116},"\u002Farchives\u002Fmybaitsplus-common-annotation","本文主要带大家来看下 Mybatis Plus 框架中，使用频率非常高的几个注解及其属性值，因为编写此本教程目的是为了大家快速入门并使用 Mybatis Plus，关于注解更高级的用法请参考官网...","2026-09-13T05:25:33.983128Z",[459],{"metadata":460,"spec":461,"status":462,"postCount":96},{"name":87,"creationTimestamp":88},{"displayName":90,"slug":87,"cover":91,"description":92,"priority":27,"hideFromList":93,"preventParentPostCascadeQuery":93},{"permalink":95,"postCount":96,"visiblePostCount":96},{"metadata":464,"spec":467,"status":476,"categories":479},{"name":465,"creationTimestamp":466},"post-mybaitsplus-code-generator-c984d27c","2026-09-12T08:29:55.452199Z",{"title":468,"slug":469,"cover":470,"excerpt":471,"publishTime":473,"categories":474,"tags":475,"priority":27,"pinned":93,"deleted":93,"visible":111,"allowComment":112},"Mybatis Plus 代码生成器（图文讲解）","mybaitsplus-code-generator","\u002Fupload\u002F167387297654896-aKtE.jpg",{"raw":472,"autoGenerate":93},"本小节中，我们将学习如何使用 Mybatis Plus 的代码生成器。可能有效小伙伴会疑惑，这玩意是干嘛使的？通常在实际项目开发中，如果开发一个功能，我们会先进行表设计，技术方案的确定，技术经理评估 OK 以后，才会进行项目开发，而不是一上来就写代码，跟无头苍蝇一样...","2026-09-12T08:29:55.508709Z",[87],[],{"permalink":477,"excerpt":472,"lastModifyTime":478,"phase":116},"\u002Farchives\u002Fmybaitsplus-code-generator","2026-09-13T05:25:35.131214Z",[480],{"metadata":481,"spec":482,"status":483,"postCount":96},{"name":87,"creationTimestamp":88},{"displayName":90,"slug":87,"cover":91,"description":92,"priority":27,"hideFromList":93,"preventParentPostCascadeQuery":93},{"permalink":95,"postCount":96,"visiblePostCount":96},{"metadata":485,"spec":486,"status":490,"categories":491,"content":496},{"name":358,"creationTimestamp":359},{"title":361,"slug":362,"cover":363,"excerpt":487,"publishTime":366,"categories":488,"tags":489,"priority":27,"pinned":93,"deleted":93,"visible":111,"allowComment":112},{"raw":365,"autoGenerate":93},[87],[],{"permalink":370,"excerpt":365,"lastModifyTime":371,"phase":116},[492],{"metadata":493,"spec":494,"status":495,"postCount":96},{"name":87,"creationTimestamp":88},{"displayName":90,"slug":87,"cover":91,"description":92,"priority":27,"hideFromList":93,"preventParentPostCascadeQuery":93},{"permalink":95,"postCount":96,"visiblePostCount":96},{"content":497,"raw":498},"\u003Cp>\u003C\u002Fp>\n\u003Cp>本小节中，我们将学习如何通过 Mybatis Plus 查询数据库表中的数据。\u003C\u002Fp>\n\u003Ch2>表结构\u003C\u002Fh2>\n\u003Cp>在前面小节中，我们已经定义好了一个用于测试的用户表， 执行脚本如下：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>DROP TABLE IF EXISTS user;\n\nCREATE TABLE `user` (\n  `id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '主键ID',\n  `name` varchar(30) NOT NULL DEFAULT '' COMMENT '姓名',\n  `age` int(11) NULL DEFAULT NULL COMMENT '年龄',\n  `gender` tinyint(2) NOT NULL DEFAULT 0 COMMENT '性别，0：女 1：男',\n  PRIMARY KEY (`id`)\n) COMMENT = '用户表';\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch2>定义实体类\u003C\u002Fh2>\n\u003Cp>定义一个名为 \u003Ccode>User\u003C\u002Fcode> 实体类：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>@TableName("user")\npublic class User {\n    \u002F**\n     * 主键 ID, @TableId 注解定义字段为表的主键，type 表示主键类型，IdType.AUTO 表示随着数据库 ID 自增\n     *\u002F\n    @TableId(type = IdType.AUTO)\n    private Long id;\n    \u002F**\n     * 姓名\n     *\u002F\n    private String name;\n    \u002F**\n     * 年龄\n     *\u002F\n    private Integer age;\n    \u002F**\n     * 性别\n     *\u002F\n    private Integer gender;\n}\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>不明白 Mybatis Plus 实体类注解的小伙伴，可参考前面小节\u003Cspan>\u003Csvg xmlns=\"http:\u002F\u002Fwww.w3.org\u002F2000\u002Fsvg\" style=\"color: #aaa; margin-left: 3px;\" aria-hidden=\"true\" focusable=\"false\" x=\"0px\" y=\"0px\" viewBox=\"0 0 100 100\" width=\"15\" height=\"15\" class=\"icon outbound\">\u003Cpath fill=\"currentColor\" d=\"M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z\">\u003C\u002Fpath> \u003Cpolygon fill=\"currentColor\" points=\"45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9\">\u003C\u002Fpolygon>\u003C\u002Fsvg> \u003Cspan class=\"sr-only\">\u003C\u002Fspan>\u003C\u002Fspan>, 有详细解释。\u003C\u002Fp>\n\u003Ch2>开始查询数据\u003C\u002Fh2>\n\u003Cp>Mybatis Plus 对 Mapper 层和 Service 层都将常见的增删改查操作封装好了，只需简单的继承，即可轻松搞定对数据的增删改查，本文重点讲解查询相关的部分。\u003C\u002Fp>\n\u003Ch3>Mapper 层\u003C\u002Fh3>\n\u003Cp>定义一个 \u003Ccode>UserMapper\u003C\u002Fcode> , 让其继承自 \u003Ccode>BaseMapper\u003C\u002Fcode> :\u003C\u002Fp>\n\u003Cpre>\u003Ccode>public interface UserMapper extends BaseMapper<User> {\n}\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>然后，注入 Mapper :\u003C\u002Fp>\n\u003Cpre>\u003Ccode>@Autowired\nprivate UserMapper userMapper;\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>\u003Ccode>BaseMapper\u003C\u002Fcode> 提供的查询相关的方法如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cimg src=\"\u002Fupload\u002F167238066532413-dlWV.jpg\" loading=\"lazy\">\n\u003C\u002Fp>\n\u003Cp>解释一下每个方法的作用：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 根据 ID 查询\nT selectById(Serializable id);\n\u002F\u002F 通过 Wrapper 组装查询条件，查询一条记录\nT selectOne(Wrapper<T> queryWrapper);\n\n\u002F\u002F 查询（根据ID 批量查询）\nList<T> selectBatchIds(Collection<? extends Serializable> idList);\n\u002F\u002F 通过 Wrapper 组装查询条件，查询全部记录\nList<T> selectList(Wrapper<T> queryWrapper);\n\u002F\u002F 查询（根据 columnMap 来设置条件）\nList<T> selectByMap(Map<String, Object> columnMap);\n\u002F\u002F 根据 Wrapper 组装查询条件，查询全部记录，并以 map 的形式返回\nList<Map<String, Object>> selectMaps(Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值\nList<Object> selectObjs(Wrapper<T> queryWrapper);\n\n\u002F\u002F =========================== 分页相关 ===========================\n\u002F\u002F 根据 entity 条件，查询全部记录（并翻页）\nIPage<T> selectPage(IPage<T> page, Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper 条件，查询全部记录（并翻页）\nIPage<Map<String, Object>> selectMapsPage(IPage<T> page, Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper 条件，查询总记录数\nInteger selectCount(Wrapper<T> queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Serializable\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>id\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 ID\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类（可以为 null）\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Collection<? extends Serializable>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>idList\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 ID 列表(不能为 null 以及 empty)\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Map<String, Object>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>columnMap\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">表字段 map 对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>IPage<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>page\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">分页查询条件（可以为 RowBounds.DEFAULT）\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch4>示例代码\u003C\u002Fh4>\n\u003Cp>接下来，本文来演示一些示例代码以便你快速了解如何使用，注意，分页相关的方法暂不做讲解，后面会单独开一篇来详细讲解。\u003C\u002Fp>\n\u003Cp>1、根据 ID 查询：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id=1 \nUser user = userMapper.selectById(1L);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>2、通过 Wrapper 组装查询条件，查询一条记录:\u003C\u002Fp>\n\u003Cpre>\u003Ccode>QueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F 仅查询 id, name 字段\nqueryWrapper.select("id", "name");\n\u002F\u002F where id = 1\nqueryWrapper.eq("id", 1L);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (id = 1)\nUser user = userMapper.selectOne(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cblockquote>\n\u003Cp>注意： \u003Ccode>selectOne\u003C\u002Fcode> 方法期望仅返回一条数据，若实际查询到多条数据，会主动抛出异常，内部源码如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cimg src=\"\u002Fupload\u002F167238290868316-figO.jpg\" loading=\"lazy\">\n\u003C\u002Fp>\n\u003C\u002Fblockquote>\n\u003Cp>2、查询（根据ID 批量查询）：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id IN ( 1 , 2 , 3 )\nList<User> users = userMapper.selectBatchIds(Arrays.asList(1L, 2L, 3L));\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>3、通过 Wrapper 组装查询条件，查询全部记录:\u003C\u002Fp>\n\u003Cpre>\u003Ccode>QueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F 仅查询 id, name 字段\nqueryWrapper.select("id", "name");\n\u002F\u002F where age = 30\nqueryWrapper.eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\nList<User> users = userMapper.selectList(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>4、查询（根据 columnMap 来设置条件）：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 通过 map 来设置查询条件\nMap<String, Object> columnMap = new HashMap<>();\ncolumnMap.put("name", "张三");\ncolumnMap.put("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE name = '张三' AND age = 30\nList<User> users = userMapper.selectByMap(columnMap);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>5、根据 Wrapper 组装查询条件，查询全部记录，并以 map 的形式返回：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>QueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F 仅查询 id, name 字段\nqueryWrapper.select("id", "name");\n\u002F\u002F where age = 30\nqueryWrapper.eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\nList<Map<String,Object>> users = userMapper.selectMaps(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>6、根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>QueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F where age = 30\nqueryWrapper.eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\nList<Object> ids = userMapper.selectObjs(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>7、根据 Wrapper 条件，查询总记录数：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 组装查询条件\nQueryWrapper<User> queryWrapper = new QueryWrapper<>();\nqueryWrapper.eq("name", "张三").eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT COUNT( * ) FROM user WHERE (name = '张三' AND age = 30)\nlong count = userMapper.selectCount(queryWrapper);\n\nSystem.out.println("总记录数：" + count);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch3>Service 层\u003C\u002Fh3>\n\u003Cp>Mybatis Plus 同样也封装了通用的 Service 层 CRUD 操作，并且提供了更丰富的方法。接下来，我们上手看 Service 层的代码结构，如下图：\u003C\u002Fp>\n\u003Cp>\n\u003Cimg src=\"\u002Fupload\u002F167204808139593-dWMf.jpg\" loading=\"lazy\" title=\"定义 Service 层\" alt=\"定义 Service 层\">\u003Cspan class=\"image-caption\">定义 Service 层\u003C\u002Fspan>\n\u003C\u002Fp>\n\u003Cp>先定义 \u003Ccode>UserService\u003C\u002Fcode> 接口 ，让其继承自 \u003Ccode>IService\u003C\u002Fcode>:\u003C\u002Fp>\n\u003Cpre>\u003Ccode>public interface UserService extends IService<User> {\n}\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>再定义实现类 \u003Ccode>UserServiceImpl\u003C\u002Fcode>，让其继承自 \u003Ccode>ServiceImpl\u003C\u002Fcode>, 同时实现 \u003Ccode>UserService\u003C\u002Fcode> 接口，这样就可以让 \u003Ccode>UserService\u003C\u002Fcode> 拥有了基础通用的 CRUD 功能，当然，实际开发中，业务会更加复杂，就需要向 \u003Ccode>IService\u003C\u002Fcode> 接口自定义方法并实现:\u003C\u002Fp>\n\u003Cpre>\u003Ccode>@Service\npublic class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {\n}\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>注入 \u003Ccode>UserService\u003C\u002Fcode> :\u003C\u002Fp>\n\u003Cpre>\u003Ccode>@Autowired\nprivate UserService userService;\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>Service 层封装的查询方法注意分为 4 块：\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Ccode>getXXX\u003C\u002Fcode> : get 开头的方法；\u003C\u002Fli>\n\u003Cli>\u003Ccode>listXXX\u003C\u002Fcode> : list 开头的方法，用于查询多条数据；\u003C\u002Fli>\n\u003Cli>\u003Ccode>pageXXX\u003C\u002Fcode> : page 开头的方法，用于分页查询；\u003C\u002Fli>\n\u003Cli>\u003Ccode>count\u003C\u002Fcode> : 用于查询总记录数；\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>接下来，我们一一讲解。\u003C\u002Fp>\n\u003Ch4>get 相关方法\u003C\u002Fh4>\n\u003Cp>\u003Ccode>get\u003C\u002Fcode>  开头的相关方法用于查询一条记录，方法如下：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 根据 ID 查询\nT getById(Serializable id);\n\u002F\u002F 根据 Wrapper，查询一条记录。如果结果集是多个会抛出异常\nT getOne(Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper，查询一条记录\nT getOne(Wrapper<T> queryWrapper, boolean throwEx);\n\u002F\u002F 根据 Wrapper，查询一条记录，以 map 的形式返回数据\nMap<String, Object> getMap(Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper，查询一条记录\n<V> V getObj(Wrapper<T> queryWrapper, Function<? super Object, V> mapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Serializable\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>id\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 \u003Ccode>ID\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类 \u003Ccode>QueryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>boolean\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>throwEx\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">有多个 result 是否抛出异常\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>T\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>entity\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Function<? super Object, V>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>mapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">转换函数\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch5>示例代码\u003C\u002Fh5>\n\u003Cp>这里挑两个具有代表性的方法：\u003C\u002Fp>\n\u003Col>\n\u003Cli>根据 ID 查询\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cpre>\u003Ccode>\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id=1        \nUser user = userService.getById(1L);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Col start=\"2\">\n\u003Cli>根据 Wrapper，查询一条记录。如果结果集是多个会抛出异常：\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cpre>\u003Ccode>\u002F\u002F 组装查询条件\nQueryWrapper<User> queryWrapper = new QueryWrapper<>();\nqueryWrapper.eq("id", 1L).eq("name", "张三");\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (id = 1 AND name = '张三')\nUser user = userService.getOne(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch4>list 相关方法\u003C\u002Fh4>\n\u003Cp>\u003Ccode>list\u003C\u002Fcode>  开头的相关方法用于查询多条记录，方法如下：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 查询所有\nList<T> list();\n\u002F\u002F 查询列表\nList<T> list(Wrapper<T> queryWrapper);\n\u002F\u002F 查询（根据ID 批量查询）\nCollection<T> listByIds(Collection<? extends Serializable> idList);\n\u002F\u002F 查询（根据 columnMap 条件）\nCollection<T> listByMap(Map<String, Object> columnMap);\n\u002F\u002F 查询所有列表, 以 map 的形式返回\nList<Map<String, Object>> listMaps();\n\u002F\u002F 查询列表\nList<Map<String, Object>> listMaps(Wrapper<T> queryWrapper);\n\u002F\u002F 查询全部记录\nList<Object> listObjs();\n\u002F\u002F 查询全部记录\n<V> List<V> listObjs(Function<? super Object, V> mapper);\n\u002F\u002F 根据 Wrapper 条件，查询全部记录\nList<Object> listObjs(Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper 条件，查询全部记录\n<V> List<V> listObjs(Wrapper<T> queryWrapper, Function<? super Object, V> mapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类 \u003Ccode>QueryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Collection<? extends Serializable>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>idList\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 \u003Ccode>ID\u003C\u002Fcode> 列表\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Map<String, Object>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>columnMap\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">表字段 \u003Ccode>map\u003C\u002Fcode> 对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Function<? super Object, V>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>mapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">转换函数\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch5>示例代码\u003C\u002Fh5>\n\u003Cp>这里挑几个具有代表性的方法：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 组装查询条件\nQueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F where name = '张三' and age >= 20\nqueryWrapper.eq("name", "张三").ge("age", 20);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (name = '张三' AND age >= 20)\nList<User> users = userService.list(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cpre>\u003Ccode>\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id IN ( 1 , 2 , 3 )\nList<User> users = userService.listByIds(Arrays.asList(1L, 2L, 3L));\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cpre>\u003Ccode>Map<String , Object> columnMap = new HashMap<>();\ncolumnMap.put("name", "张三");\ncolumnMap.put("age", 30L);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE name = '张三' AND age = 30\nList<User> users = userService.listByMap(columnMap);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch4>page 分页相关方法\u003C\u002Fh4>\n\u003Cp>放到后面《分页查询》\u003Cspan>\u003Csvg xmlns=\"http:\u002F\u002Fwww.w3.org\u002F2000\u002Fsvg\" style=\"color: #aaa; margin-left: 3px;\" aria-hidden=\"true\" focusable=\"false\" x=\"0px\" y=\"0px\" viewBox=\"0 0 100 100\" width=\"15\" height=\"15\" class=\"icon outbound\">\u003Cpath fill=\"currentColor\" d=\"M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z\">\u003C\u002Fpath> \u003Cpolygon fill=\"currentColor\" points=\"45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9\">\u003C\u002Fpolygon>\u003C\u002Fsvg> \u003Cspan class=\"sr-only\">\u003C\u002Fspan>\u003C\u002Fspan>小节统一讲解；\u003C\u002Fp>\n\u003Ch4>count 查询总记录数\u003C\u002Fh4>\n\u003Cp>查询总记录数 \u003Ccode>count\u003C\u002Fcode> 相关方法如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cimg src=\"\u002Fupload\u002F167248996956072-csmW.jpg\" loading=\"lazy\">\n\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 查询总记录数（不带查询条件）\ncount();\n\u002F\u002F 查询总记录数（可以带查询条件）\ncount(Wrapper<T>)\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch5>示例代码\u003C\u002Fh5>\n\u003Cpre>\u003Ccode>\u002F\u002F 组装查询条件\nQueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F where age = 30\nqueryWrapper.eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT COUNT( * ) FROM user WHERE (age = 30)\nlong count = userService.count(queryWrapper);\nSystem.out.println("总记录数：" + count);\n\u003C\u002Fcode>\u003C\u002Fpre>\n13:T103a5,\u003Cp>\u003C\u002Fp>\n\u003Cp>本小节中，我们将学习如何通过 Mybatis Plus 查询数据库表中的数据。\u003C\u002Fp>\n\u003Ch2 id=\"toc-0\">表结构\u003C\u002Fh2>\n\u003Cp>在前面小节中，我们已经定义好了一个用于测试的用户表， 执行脚本如下：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"DROP%20TABLE%20IF%20EXISTS%20user%3B%0A%0ACREATE%20TABLE%20%60user%60%20(%0A%20%20%60id%60%20bigint(20)%20UNSIGNED%20NOT%20NULL%20AUTO_INCREMENT%20COMMENT%20'%E4%B8%BB%E9%94%AEID'%2C%0A%20%20%60name%60%20varchar(30)%20NOT%20NULL%20DEFAULT%20''%20COMMENT%20'%E5%A7%93%E5%90%8D'%2C%0A%20%20%60age%60%20int(11)%20NULL%20DEFAULT%20NULL%20COMMENT%20'%E5%B9%B4%E9%BE%84'%2C%0A%20%20%60gender%60%20tinyint(2)%20NOT%20NULL%20DEFAULT%200%20COMMENT%20'%E6%80%A7%E5%88%AB%EF%BC%8C0%EF%BC%9A%E5%A5%B3%201%EF%BC%9A%E7%94%B7'%2C%0A%20%20PRIMARY%20KEY%20(%60id%60)%0A)%20COMMENT%20%3D%20'%E7%94%A8%E6%88%B7%E8%A1%A8'%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token keyword\">DROP\u003C\u002Fspan> \u003Cspan class=\"token keyword\">TABLE\u003C\u002Fspan> \u003Cspan class=\"token keyword\">IF\u003C\u002Fspan> \u003Cspan class=\"token keyword\">EXISTS\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token keyword\">CREATE\u003C\u002Fspan> \u003Cspan class=\"token keyword\">TABLE\u003C\u002Fspan> \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>user\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\n  \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>id\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">bigint\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">20\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token keyword\">UNSIGNED\u003C\u002Fspan> \u003Cspan class=\"token operator\">NOT\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">AUTO_INCREMENT\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token string\">'主键ID'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>\n  \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>name\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">varchar\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token operator\">NOT\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">DEFAULT\u003C\u002Fspan> \u003Cspan class=\"token string\">''\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token string\">'姓名'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>\n  \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>age\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">int\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">11\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">DEFAULT\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token string\">'年龄'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>\n  \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>gender\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">tinyint\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">2\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token operator\">NOT\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">DEFAULT\u003C\u002Fspan> \u003Cspan class=\"token number\">0\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token string\">'性别，0：女 1：男'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>\n  \u003Cspan class=\"token keyword\">PRIMARY\u003C\u002Fspan> \u003Cspan class=\"token keyword\">KEY\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>id\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> \u003Cspan class=\"token string\">'用户表'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Ch2 id=\"toc-1\">定义实体类\u003C\u002Fh2>\n\u003Cp>定义一个名为 \u003Ccode>User\u003C\u002Fcode> 实体类：\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%40TableName(%22user%22)%0Apublic%20class%20User%20%7B%0A%20%20%20%20%2F**%0A%20%20%20%20%20*%20%E4%B8%BB%E9%94%AE%20ID%2C%20%40TableId%20%E6%B3%A8%E8%A7%A3%E5%AE%9A%E4%B9%89%E5%AD%97%E6%AE%B5%E4%B8%BA%E8%A1%A8%E7%9A%84%E4%B8%BB%E9%94%AE%EF%BC%8Ctype%20%E8%A1%A8%E7%A4%BA%E4%B8%BB%E9%94%AE%E7%B1%BB%E5%9E%8B%EF%BC%8CIdType.AUTO%20%E8%A1%A8%E7%A4%BA%E9%9A%8F%E7%9D%80%E6%95%B0%E6%8D%AE%E5%BA%93%20ID%20%E8%87%AA%E5%A2%9E%0A%20%20%20%20%20*%2F%0A%20%20%20%20%40TableId(type%20%3D%20IdType.AUTO)%0A%20%20%20%20private%20Long%20id%3B%0A%20%20%20%20%2F**%0A%20%20%20%20%20*%20%E5%A7%93%E5%90%8D%0A%20%20%20%20%20*%2F%0A%20%20%20%20private%20String%20name%3B%0A%20%20%20%20%2F**%0A%20%20%20%20%20*%20%E5%B9%B4%E9%BE%84%0A%20%20%20%20%20*%2F%0A%20%20%20%20private%20Integer%20age%3B%0A%20%20%20%20%2F**%0A%20%20%20%20%20*%20%E6%80%A7%E5%88%AB%0A%20%20%20%20%20*%2F%0A%20%20%20%20private%20Integer%20gender%3B%0A%7D%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token annotation punctuation\">@TableName\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"user\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">public\u003C\u002Fspan> \u003Cspan class=\"token keyword\">class\u003C\u002Fspan> \u003Cspan class=\"token class-name\">User\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">{\u003C\u002Fspan>\n    \u003Cspan class=\"token comment\">\u002F**\n     * 主键 ID, @TableId 注解定义字段为表的主键，type 表示主键类型，IdType.AUTO 表示随着数据库 ID 自增\n     *\u002F\u003C\u002Fspan>\n    \u003Cspan class=\"token annotation punctuation\">@TableId\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>type \u003Cspan class=\"token operator\">=\u003C\u002Fspan> \u003Cspan class=\"token class-name\">IdType\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token constant\">AUTO\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\n    \u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Long\u003C\u002Fspan> id\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n    \u003Cspan class=\"token comment\">\u002F**\n     * 姓名\n     *\u002F\u003C\u002Fspan>\n    \u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">String\u003C\u002Fspan> name\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n    \u003Cspan class=\"token comment\">\u002F**\n     * 年龄\n     *\u002F\u003C\u002Fspan>\n    \u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Integer\u003C\u002Fspan> age\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n    \u003Cspan class=\"token comment\">\u002F**\n     * 性别\n     *\u002F\u003C\u002Fspan>\n    \u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Integer\u003C\u002Fspan> gender\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">}\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>不明白 Mybatis Plus 实体类注解的小伙伴，可参考前面小节\u003Cspan>\u003Csvg xmlns=\"http:\u002F\u002Fwww.w3.org\u002F2000\u002Fsvg\" style=\"color: #aaa; margin-left: 3px;\" aria-hidden=\"true\" focusable=\"false\" x=\"0px\" y=\"0px\" viewBox=\"0 0 100 100\" width=\"15\" height=\"15\" class=\"icon outbound\">\u003Cpath fill=\"currentColor\" d=\"M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z\">\u003C\u002Fpath> \u003Cpolygon fill=\"currentColor\" points=\"45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9\">\u003C\u002Fpolygon>\u003C\u002Fsvg> \u003Cspan class=\"sr-only\">\u003C\u002Fspan>\u003C\u002Fspan>, 有详细解释。\u003C\u002Fp>\n\u003Ch2 id=\"toc-2\">开始查询数据\u003C\u002Fh2>\n\u003Cp>Mybatis Plus 对 Mapper 层和 Service 层都将常见的增删改查操作封装好了，只需简单的继承，即可轻松搞定对数据的增删改查，本文重点讲解查询相关的部分。\u003C\u002Fp>\n\u003Ch3 id=\"toc-3\">Mapper 层\u003C\u002Fh3>\n\u003Cp>定义一个 \u003Ccode>UserMapper\u003C\u002Fcode> , 让其继承自 \u003Ccode>BaseMapper\u003C\u002Fcode> :\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"public%20interface%20UserMapper%20extends%20BaseMapper%3CUser%3E%20%7B%0A%7D%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token keyword\">public\u003C\u002Fspan> \u003Cspan class=\"token keyword\">interface\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserMapper\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">BaseMapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">User\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">{\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">}\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>然后，注入 Mapper :\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%40Autowired%0Aprivate%20UserMapper%20userMapper%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token annotation punctuation\">@Autowired\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserMapper\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>\u003Ccode>BaseMapper\u003C\u002Fcode> 提供的查询相关的方法如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cdiv class=\"img-loading\">\u003Cimg src=\"\u002Fupload\u002F167238066532413-dlWV.jpg\" loading=\"lazy\">\u003C\u002Fdiv>\n\u003C\u002Fp>\n\u003Cp>解释一下每个方法的作用：\u003C\u002Fp>\n\u003Cdiv class=\"language-javascript\" data-ext=\"javascript\" data-code=\"%2F%2F%20%E6%A0%B9%E6%8D%AE%20ID%20%E6%9F%A5%E8%AF%A2%0AT%20selectById(Serializable%20id)%3B%0A%2F%2F%20%E9%80%9A%E8%BF%87%20Wrapper%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%0AT%20selectOne(Wrapper%3CT%3E%20queryWrapper)%3B%0A%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%EF%BC%88%E6%A0%B9%E6%8D%AEID%20%E6%89%B9%E9%87%8F%E6%9F%A5%E8%AF%A2%EF%BC%89%0AList%3CT%3E%20selectBatchIds(Collection%3C%3F%20extends%20Serializable%3E%20idList)%3B%0A%2F%2F%20%E9%80%9A%E8%BF%87%20Wrapper%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0AList%3CT%3E%20selectList(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%EF%BC%88%E6%A0%B9%E6%8D%AE%20columnMap%20%E6%9D%A5%E8%AE%BE%E7%BD%AE%E6%9D%A1%E4%BB%B6%EF%BC%89%0AList%3CT%3E%20selectByMap(Map%3CString%2C%20Object%3E%20columnMap)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%EF%BC%8C%E5%B9%B6%E4%BB%A5%20map%20%E7%9A%84%E5%BD%A2%E5%BC%8F%E8%BF%94%E5%9B%9E%0AList%3CMap%3CString%2C%20Object%3E%3E%20selectMaps(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%E3%80%82%E6%B3%A8%E6%84%8F%EF%BC%9A%20%E5%8F%AA%E8%BF%94%E5%9B%9E%E7%AC%AC%E4%B8%80%E4%B8%AA%E5%AD%97%E6%AE%B5%E7%9A%84%E5%80%BC%0AList%3CObject%3E%20selectObjs(Wrapper%3CT%3E%20queryWrapper)%3B%0A%0A%2F%2F%20%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%20%E5%88%86%E9%A1%B5%E7%9B%B8%E5%85%B3%20%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20entity%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%EF%BC%88%E5%B9%B6%E7%BF%BB%E9%A1%B5%EF%BC%89%0AIPage%3CT%3E%20selectPage(IPage%3CT%3E%20page%2C%20Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%EF%BC%88%E5%B9%B6%E7%BF%BB%E9%A1%B5%EF%BC%89%0AIPage%3CMap%3CString%2C%20Object%3E%3E%20selectMapsPage(IPage%3CT%3E%20page%2C%20Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E6%80%BB%E8%AE%B0%E5%BD%95%E6%95%B0%0AInteger%20selectCount(Wrapper%3CT%3E%20queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-javascript\">\u003Cspan class=\"token comment\">\u002F\u002F 根据 ID 查询\u003C\u002Fspan>\n\u003Cspan class=\"token constant\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">selectById\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Serializable id\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 通过 Wrapper 组装查询条件，查询一条记录\u003C\u002Fspan>\n\u003Cspan class=\"token constant\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">selectOne\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 查询（根据ID 批量查询）\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectBatchIds\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Collection\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Serializable\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> idList\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 通过 Wrapper 组装查询条件，查询全部记录\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectList\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询（根据 columnMap 来设置条件）\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectByMap\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> columnMap\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 组装查询条件，查询全部记录，并以 map 的形式返回\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectMaps\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F =========================== 分页相关 ===========================\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 entity 条件，查询全部记录（并翻页）\u003C\u002Fspan>\nIPage\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectPage\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>IPage\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> page\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询全部记录（并翻页）\u003C\u002Fspan>\nIPage\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectMapsPage\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>IPage\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> page\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询总记录数\u003C\u002Fspan>\nInteger \u003Cspan class=\"token function\">selectCount\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Serializable\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>id\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 ID\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类（可以为 null）\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Collection<? extends Serializable>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>idList\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 ID 列表(不能为 null 以及 empty)\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Map<String, Object>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>columnMap\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">表字段 map 对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>IPage<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>page\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">分页查询条件（可以为 RowBounds.DEFAULT）\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch4 id=\"toc-4\">示例代码\u003C\u002Fh4>\n\u003Cp>接下来，本文来演示一些示例代码以便你快速了解如何使用，注意，分页相关的方法暂不做讲解，后面会单独开一篇来详细讲解。\u003C\u002Fp>\n\u003Cp>1、根据 ID 查询：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20id%3D1%20%0AUser%20user%20%3D%20userMapper.selectById(1L)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id=1 \u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">User\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectById\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>2、通过 Wrapper 组装查询条件，查询一条记录:\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"QueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20%E4%BB%85%E6%9F%A5%E8%AF%A2%20id%2C%20name%20%E5%AD%97%E6%AE%B5%0AqueryWrapper.select(%22id%22%2C%20%22name%22)%3B%0A%2F%2F%20where%20id%20%3D%201%0AqueryWrapper.eq(%22id%22%2C%201L)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20(id%20%3D%201)%0AUser%20user%20%3D%20userMapper.selectOne(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">QueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 仅查询 id, name 字段\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token keyword\">select\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where id = 1\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (id = 1)\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">User\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectOne\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cblockquote>\n\u003Cp>注意： \u003Ccode>selectOne\u003C\u002Fcode> 方法期望仅返回一条数据，若实际查询到多条数据，会主动抛出异常，内部源码如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cdiv class=\"img-loading\">\u003Cimg src=\"\u002Fupload\u002F167238290868316-figO.jpg\" loading=\"lazy\">\u003C\u002Fdiv>\n\u003C\u002Fp>\n\u003C\u002Fblockquote>\n\u003Cp>2、查询（根据ID 批量查询）：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20id%20IN%20(%201%20%2C%202%20%2C%203%20)%0AList%3CUser%3E%20users%20%3D%20userMapper.selectBatchIds(Arrays.asList(1L%2C%202L%2C%203L))%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id IN ( 1 , 2 , 3 )\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectBatchIds\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Arrays\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>asList\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">2\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">3\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>3、通过 Wrapper 组装查询条件，查询全部记录:\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"QueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20%E4%BB%85%E6%9F%A5%E8%AF%A2%20id%2C%20name%20%E5%AD%97%E6%AE%B5%0AqueryWrapper.select(%22id%22%2C%20%22name%22)%3B%0A%2F%2F%20where%20age%20%3D%2030%0AqueryWrapper.eq(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%20FROM%20user%20WHERE%20(age%20%3D%2030)%0AList%3CUser%3E%20users%20%3D%20userMapper.selectList(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">QueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 仅查询 id, name 字段\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token keyword\">select\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where age = 30\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectList\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>4、查询（根据 columnMap 来设置条件）：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E9%80%9A%E8%BF%87%20map%20%E6%9D%A5%E8%AE%BE%E7%BD%AE%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%0AMap%3CString%2C%20Object%3E%20columnMap%20%3D%20new%20HashMap%3C%3E()%3B%0AcolumnMap.put(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22)%3B%0AcolumnMap.put(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20name%20%3D%20'%E5%BC%A0%E4%B8%89'%20AND%20age%20%3D%2030%0AList%3CUser%3E%20users%20%3D%20userMapper.selectByMap(columnMap)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 通过 map 来设置查询条件\u003C\u002Fspan>\nMap\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> columnMap \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new HashMap\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\ncolumnMap\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>put\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\ncolumnMap\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>put\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE name = '张三' AND age = 30\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectByMap\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>columnMap\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>5、根据 Wrapper 组装查询条件，查询全部记录，并以 map 的形式返回：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"QueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20%E4%BB%85%E6%9F%A5%E8%AF%A2%20id%2C%20name%20%E5%AD%97%E6%AE%B5%0AqueryWrapper.select(%22id%22%2C%20%22name%22)%3B%0A%2F%2F%20where%20age%20%3D%2030%0AqueryWrapper.eq(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%20FROM%20user%20WHERE%20(age%20%3D%2030)%0AList%3CMap%3CString%2CObject%3E%3E%20users%20%3D%20userMapper.selectMaps(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">QueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 仅查询 id, name 字段\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token keyword\">select\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where age = 30\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectMaps\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>6、根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"QueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20where%20age%20%3D%2030%0AqueryWrapper.eq(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%20FROM%20user%20WHERE%20(age%20%3D%2030)%0AList%3CObject%3E%20ids%20%3D%20userMapper.selectObjs(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">QueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where age = 30\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> ids \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectObjs\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>7、根据 Wrapper 条件，查询总记录数：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%0AQueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0AqueryWrapper.eq(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22).eq(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20COUNT(%20*%20)%20FROM%20user%20WHERE%20(name%20%3D%20'%E5%BC%A0%E4%B8%89'%20AND%20age%20%3D%2030)%0Along%20count%20%3D%20userMapper.selectCount(queryWrapper)%3B%0A%0ASystem.out.println(%22%E6%80%BB%E8%AE%B0%E5%BD%95%E6%95%B0%EF%BC%9A%22%20%2B%20count)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 组装查询条件\u003C\u002Fspan>\nQueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT COUNT( * ) FROM user WHERE (name = '张三' AND age = 30)\u003C\u002Fspan>\nlong count \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectCount\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\nSystem\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token keyword\">out\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>println\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"总记录数：\"\u003C\u002Fspan> \u003Cspan class=\"token operator\">+\u003C\u002Fspan> count\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Ch3 id=\"toc-5\">Service 层\u003C\u002Fh3>\n\u003Cp>Mybatis Plus 同样也封装了通用的 Service 层 CRUD 操作，并且提供了更丰富的方法。接下来，我们上手看 Service 层的代码结构，如下图：\u003C\u002Fp>\n\u003Cp>\n\u003Cdiv class=\"img-loading\">\u003Cimg src=\"\u002Fupload\u002F167204808139593-dWMf.jpg\" loading=\"lazy\" title=\"定义 Service 层\" alt=\"定义 Service 层\">\u003C\u002Fdiv>\u003Cspan class=\"image-caption\">定义 Service 层\u003C\u002Fspan>\n\u003C\u002Fp>\n\u003Cp>先定义 \u003Ccode>UserService\u003C\u002Fcode> 接口 ，让其继承自 \u003Ccode>IService\u003C\u002Fcode>:\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"public%20interface%20UserService%20extends%20IService%3CUser%3E%20%7B%0A%7D%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token keyword\">public\u003C\u002Fspan> \u003Cspan class=\"token keyword\">interface\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserService\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">IService\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">User\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">{\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">}\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>再定义实现类 \u003Ccode>UserServiceImpl\u003C\u002Fcode>，让其继承自 \u003Ccode>ServiceImpl\u003C\u002Fcode>, 同时实现 \u003Ccode>UserService\u003C\u002Fcode> 接口，这样就可以让 \u003Ccode>UserService\u003C\u002Fcode> 拥有了基础通用的 CRUD 功能，当然，实际开发中，业务会更加复杂，就需要向 \u003Ccode>IService\u003C\u002Fcode> 接口自定义方法并实现:\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%40Service%0Apublic%20class%20UserServiceImpl%20extends%20ServiceImpl%3CUserMapper%2C%20User%3E%20implements%20UserService%20%7B%0A%7D%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token annotation punctuation\">@Service\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">public\u003C\u002Fspan> \u003Cspan class=\"token keyword\">class\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserServiceImpl\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">ServiceImpl\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">UserMapper\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token class-name\">User\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">implements\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserService\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">{\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">}\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>注入 \u003Ccode>UserService\u003C\u002Fcode> :\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%40Autowired%0Aprivate%20UserService%20userService%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token annotation punctuation\">@Autowired\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserService\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>Service 层封装的查询方法注意分为 4 块：\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Ccode>getXXX\u003C\u002Fcode> : get 开头的方法；\u003C\u002Fli>\n\u003Cli>\u003Ccode>listXXX\u003C\u002Fcode> : list 开头的方法，用于查询多条数据；\u003C\u002Fli>\n\u003Cli>\u003Ccode>pageXXX\u003C\u002Fcode> : page 开头的方法，用于分页查询；\u003C\u002Fli>\n\u003Cli>\u003Ccode>count\u003C\u002Fcode> : 用于查询总记录数；\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>接下来，我们一一讲解。\u003C\u002Fp>\n\u003Ch4 id=\"toc-6\">get 相关方法\u003C\u002Fh4>\n\u003Cp>\u003Ccode>get\u003C\u002Fcode>  开头的相关方法用于查询一条记录，方法如下：\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%2F%2F%20%E6%A0%B9%E6%8D%AE%20ID%20%E6%9F%A5%E8%AF%A2%0AT%20getById(Serializable%20id)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%E3%80%82%E5%A6%82%E6%9E%9C%E7%BB%93%E6%9E%9C%E9%9B%86%E6%98%AF%E5%A4%9A%E4%B8%AA%E4%BC%9A%E6%8A%9B%E5%87%BA%E5%BC%82%E5%B8%B8%0AT%20getOne(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%0AT%20getOne(Wrapper%3CT%3E%20queryWrapper%2C%20boolean%20throwEx)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%EF%BC%8C%E4%BB%A5%20map%20%E7%9A%84%E5%BD%A2%E5%BC%8F%E8%BF%94%E5%9B%9E%E6%95%B0%E6%8D%AE%0AMap%3CString%2C%20Object%3E%20getMap(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%0A%3CV%3E%20V%20getObj(Wrapper%3CT%3E%20queryWrapper%2C%20Function%3C%3F%20super%20Object%2C%20V%3E%20mapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token comment\">\u002F\u002F 根据 ID 查询\u003C\u002Fspan>\n\u003Cspan class=\"token class-name\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">getById\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Serializable\u003C\u002Fspan> id\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper，查询一条记录。如果结果集是多个会抛出异常\u003C\u002Fspan>\n\u003Cspan class=\"token class-name\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">getOne\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Wrapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">T\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper，查询一条记录\u003C\u002Fspan>\n\u003Cspan class=\"token class-name\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">getOne\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Wrapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">T\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token keyword\">boolean\u003C\u002Fspan> throwEx\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper，查询一条记录，以 map 的形式返回数据\u003C\u002Fspan>\n\u003Cspan class=\"token class-name\">Map\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">String\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Object\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token function\">getMap\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Wrapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">T\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper，查询一条记录\u003C\u002Fspan>\n\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">V\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token class-name\">V\u003C\u002Fspan> \u003Cspan class=\"token function\">getObj\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Wrapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">T\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Function\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">super\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Object\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token class-name\">V\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> mapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Serializable\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>id\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 \u003Ccode>ID\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类 \u003Ccode>QueryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>boolean\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>throwEx\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">有多个 result 是否抛出异常\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>T\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>entity\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Function<? super Object, V>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>mapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">转换函数\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch5 id=\"toc-7\">示例代码\u003C\u002Fh5>\n\u003Cp>这里挑两个具有代表性的方法：\u003C\u002Fp>\n\u003Col>\n\u003Cli>根据 ID 查询\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20id%3D1%20%20%20%20%20%20%20%20%0AUser%20user%20%3D%20userService.getById(1L)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id=1        \u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">User\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>getById\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Col start=\"2\">\n\u003Cli>根据 Wrapper，查询一条记录。如果结果集是多个会抛出异常：\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%0AQueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0AqueryWrapper.eq(%22id%22%2C%201L).eq(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20(id%20%3D%201%20AND%20name%20%3D%20'%E5%BC%A0%E4%B8%89')%0AUser%20user%20%3D%20userService.getOne(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 组装查询条件\u003C\u002Fspan>\nQueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (id = 1 AND name = '张三')\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">User\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>getOne\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Ch4 id=\"toc-8\">list 相关方法\u003C\u002Fh4>\n\u003Cp>\u003Ccode>list\u003C\u002Fcode>  开头的相关方法用于查询多条记录，方法如下：\u003C\u002Fp>\n\u003Cdiv class=\"language-javascript\" data-ext=\"javascript\" data-code=\"%2F%2F%20%E6%9F%A5%E8%AF%A2%E6%89%80%E6%9C%89%0AList%3CT%3E%20list()%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E5%88%97%E8%A1%A8%0AList%3CT%3E%20list(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%EF%BC%88%E6%A0%B9%E6%8D%AEID%20%E6%89%B9%E9%87%8F%E6%9F%A5%E8%AF%A2%EF%BC%89%0ACollection%3CT%3E%20listByIds(Collection%3C%3F%20extends%20Serializable%3E%20idList)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%EF%BC%88%E6%A0%B9%E6%8D%AE%20columnMap%20%E6%9D%A1%E4%BB%B6%EF%BC%89%0ACollection%3CT%3E%20listByMap(Map%3CString%2C%20Object%3E%20columnMap)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E6%89%80%E6%9C%89%E5%88%97%E8%A1%A8%2C%20%E4%BB%A5%20map%20%E7%9A%84%E5%BD%A2%E5%BC%8F%E8%BF%94%E5%9B%9E%0AList%3CMap%3CString%2C%20Object%3E%3E%20listMaps()%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E5%88%97%E8%A1%A8%0AList%3CMap%3CString%2C%20Object%3E%3E%20listMaps(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0AList%3CObject%3E%20listObjs()%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0A%3CV%3E%20List%3CV%3E%20listObjs(Function%3C%3F%20super%20Object%2C%20V%3E%20mapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0AList%3CObject%3E%20listObjs(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0A%3CV%3E%20List%3CV%3E%20listObjs(Wrapper%3CT%3E%20queryWrapper%2C%20Function%3C%3F%20super%20Object%2C%20V%3E%20mapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-javascript\">\u003Cspan class=\"token comment\">\u002F\u002F 查询所有\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">list\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询列表\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">list\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询（根据ID 批量查询）\u003C\u002Fspan>\nCollection\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listByIds\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Collection\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Serializable\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> idList\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询（根据 columnMap 条件）\u003C\u002Fspan>\nCollection\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listByMap\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> columnMap\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询所有列表, 以 map 的形式返回\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> \u003Cspan class=\"token function\">listMaps\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询列表\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> \u003Cspan class=\"token function\">listMaps\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询全部记录\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询全部记录\u003C\u002Fspan>\n\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> List\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Function\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">super\u003C\u002Fspan> Object\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> mapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询全部记录\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询全部记录\u003C\u002Fspan>\n\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> List\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Function\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">super\u003C\u002Fspan> Object\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> mapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类 \u003Ccode>QueryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Collection<? extends Serializable>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>idList\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 \u003Ccode>ID\u003C\u002Fcode> 列表\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Map<String, Object>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>columnMap\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">表字段 \u003Ccode>map\u003C\u002Fcode> 对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Function<? super Object, V>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>mapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">转换函数\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch5 id=\"toc-9\">示例代码\u003C\u002Fh5>\n\u003Cp>这里挑几个具有代表性的方法：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%0AQueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20where%20name%20%3D%20'%E5%BC%A0%E4%B8%89'%20and%20age%20%3E%3D%2020%0AqueryWrapper.eq(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22).ge(%22age%22%2C%2020)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20(name%20%3D%20'%E5%BC%A0%E4%B8%89'%20AND%20age%20%3E%3D%2020)%0AList%3CUser%3E%20users%20%3D%20userService.list(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 组装查询条件\u003C\u002Fspan>\nQueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where name = '张三' and age >= 20\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>ge\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">20\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (name = '张三' AND age >= 20)\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>list\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20id%20IN%20(%201%20%2C%202%20%2C%203%20)%0AList%3CUser%3E%20users%20%3D%20userService.listByIds(Arrays.asList(1L%2C%202L%2C%203L))%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id IN ( 1 , 2 , 3 )\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>listByIds\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Arrays\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>asList\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">2\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">3\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"Map%3CString%20%2C%20Object%3E%20columnMap%20%3D%20new%20HashMap%3C%3E()%3B%0AcolumnMap.put(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22)%3B%0AcolumnMap.put(%22age%22%2C%2030L)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20name%20%3D%20'%E5%BC%A0%E4%B8%89'%20AND%20age%20%3D%2030%0AList%3CUser%3E%20users%20%3D%20userService.listByMap(columnMap)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String \u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> columnMap \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new HashMap\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\ncolumnMap\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>put\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\ncolumnMap\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>put\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE name = '张三' AND age = 30\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>listByMap\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>columnMap\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Ch4 id=\"toc-10\">page 分页相关方法\u003C\u002Fh4>\n\u003Cp>放到后面《分页查询》\u003Cspan>\u003Csvg xmlns=\"http:\u002F\u002Fwww.w3.org\u002F2000\u002Fsvg\" style=\"color: #aaa; margin-left: 3px;\" aria-hidden=\"true\" focusable=\"false\" x=\"0px\" y=\"0px\" viewBox=\"0 0 100 100\" width=\"15\" height=\"15\" class=\"icon outbound\">\u003Cpath fill=\"currentColor\" d=\"M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z\">\u003C\u002Fpath> \u003Cpolygon fill=\"currentColor\" points=\"45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9\">\u003C\u002Fpolygon>\u003C\u002Fsvg> \u003Cspan class=\"sr-only\">\u003C\u002Fspan>\u003C\u002Fspan>小节统一讲解；\u003C\u002Fp>\n\u003Ch4 id=\"toc-11\">count 查询总记录数\u003C\u002Fh4>\n\u003Cp>查询总记录数 \u003Ccode>count\u003C\u002Fcode> 相关方法如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cdiv class=\"img-loading\">\u003Cimg src=\"\u002Fupload\u002F167248996956072-csmW.jpg\" loading=\"lazy\">\u003C\u002Fdiv>\n\u003C\u002Fp>","\u003Cp>大家好。\u003C\u002Fp>\n\u003Cp>本小节中，我们将学习如何通过 Mybatis Plus 查询数据库表中的数据。\u003C\u002Fp>\n\u003Ch2>表结构\u003C\u002Fh2>\n\u003Cp>在前面小节中，我们已经定义好了一个用于测试的用户表， 执行脚本如下：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>DROP TABLE IF EXISTS user;\n\nCREATE TABLE `user` (\n  `id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '主键ID',\n  `name` varchar(30) NOT NULL DEFAULT '' COMMENT '姓名',\n  `age` int(11) NULL DEFAULT NULL COMMENT '年龄',\n  `gender` tinyint(2) NOT NULL DEFAULT 0 COMMENT '性别，0：女 1：男',\n  PRIMARY KEY (`id`)\n) COMMENT = '用户表';\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch2>定义实体类\u003C\u002Fh2>\n\u003Cp>定义一个名为 \u003Ccode>User\u003C\u002Fcode> 实体类：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>@TableName("user")\npublic class User {\n    \u002F**\n     * 主键 ID, @TableId 注解定义字段为表的主键，type 表示主键类型，IdType.AUTO 表示随着数据库 ID 自增\n     *\u002F\n    @TableId(type = IdType.AUTO)\n    private Long id;\n    \u002F**\n     * 姓名\n     *\u002F\n    private String name;\n    \u002F**\n     * 年龄\n     *\u002F\n    private Integer age;\n    \u002F**\n     * 性别\n     *\u002F\n    private Integer gender;\n}\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>不明白 Mybatis Plus 实体类注解的小伙伴，可参考前面小节\u003Cspan>\u003Csvg xmlns=\"http:\u002F\u002Fwww.w3.org\u002F2000\u002Fsvg\" style=\"color: #aaa; margin-left: 3px;\" aria-hidden=\"true\" focusable=\"false\" x=\"0px\" y=\"0px\" viewBox=\"0 0 100 100\" width=\"15\" height=\"15\" class=\"icon outbound\">\u003Cpath fill=\"currentColor\" d=\"M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z\">\u003C\u002Fpath> \u003Cpolygon fill=\"currentColor\" points=\"45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9\">\u003C\u002Fpolygon>\u003C\u002Fsvg> \u003Cspan class=\"sr-only\">\u003C\u002Fspan>\u003C\u002Fspan>, 有详细解释。\u003C\u002Fp>\n\u003Ch2>开始查询数据\u003C\u002Fh2>\n\u003Cp>Mybatis Plus 对 Mapper 层和 Service 层都将常见的增删改查操作封装好了，只需简单的继承，即可轻松搞定对数据的增删改查，本文重点讲解查询相关的部分。\u003C\u002Fp>\n\u003Ch3>Mapper 层\u003C\u002Fh3>\n\u003Cp>定义一个 \u003Ccode>UserMapper\u003C\u002Fcode> , 让其继承自 \u003Ccode>BaseMapper\u003C\u002Fcode> :\u003C\u002Fp>\n\u003Cpre>\u003Ccode>public interface UserMapper extends BaseMapper<User> {\n}\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>然后，注入 Mapper :\u003C\u002Fp>\n\u003Cpre>\u003Ccode>@Autowired\nprivate UserMapper userMapper;\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>\u003Ccode>BaseMapper\u003C\u002Fcode> 提供的查询相关的方法如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cimg src=\"\u002Fupload\u002F167238066532413-dlWV.jpg\" loading=\"lazy\">\n\u003C\u002Fp>\n\u003Cp>解释一下每个方法的作用：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 根据 ID 查询\nT selectById(Serializable id);\n\u002F\u002F 通过 Wrapper 组装查询条件，查询一条记录\nT selectOne(Wrapper<T> queryWrapper);\n\n\u002F\u002F 查询（根据ID 批量查询）\nList<T> selectBatchIds(Collection<? extends Serializable> idList);\n\u002F\u002F 通过 Wrapper 组装查询条件，查询全部记录\nList<T> selectList(Wrapper<T> queryWrapper);\n\u002F\u002F 查询（根据 columnMap 来设置条件）\nList<T> selectByMap(Map<String, Object> columnMap);\n\u002F\u002F 根据 Wrapper 组装查询条件，查询全部记录，并以 map 的形式返回\nList<Map<String, Object>> selectMaps(Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值\nList<Object> selectObjs(Wrapper<T> queryWrapper);\n\n\u002F\u002F =========================== 分页相关 ===========================\n\u002F\u002F 根据 entity 条件，查询全部记录（并翻页）\nIPage<T> selectPage(IPage<T> page, Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper 条件，查询全部记录（并翻页）\nIPage<Map<String, Object>> selectMapsPage(IPage<T> page, Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper 条件，查询总记录数\nInteger selectCount(Wrapper<T> queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Serializable\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>id\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 ID\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类（可以为 null）\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Collection<? extends Serializable>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>idList\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 ID 列表(不能为 null 以及 empty)\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Map<String, Object>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>columnMap\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">表字段 map 对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>IPage<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>page\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">分页查询条件（可以为 RowBounds.DEFAULT）\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch4>示例代码\u003C\u002Fh4>\n\u003Cp>接下来，本文来演示一些示例代码以便你快速了解如何使用，注意，分页相关的方法暂不做讲解，后面会单独开一篇来详细讲解。\u003C\u002Fp>\n\u003Cp>1、根据 ID 查询：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id=1 \nUser user = userMapper.selectById(1L);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>2、通过 Wrapper 组装查询条件，查询一条记录:\u003C\u002Fp>\n\u003Cpre>\u003Ccode>QueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F 仅查询 id, name 字段\nqueryWrapper.select("id", "name");\n\u002F\u002F where id = 1\nqueryWrapper.eq("id", 1L);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (id = 1)\nUser user = userMapper.selectOne(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cblockquote>\n\u003Cp>注意： \u003Ccode>selectOne\u003C\u002Fcode> 方法期望仅返回一条数据，若实际查询到多条数据，会主动抛出异常，内部源码如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cimg src=\"\u002Fupload\u002F167238290868316-figO.jpg\" loading=\"lazy\">\n\u003C\u002Fp>\n\u003C\u002Fblockquote>\n\u003Cp>2、查询（根据ID 批量查询）：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id IN ( 1 , 2 , 3 )\nList<User> users = userMapper.selectBatchIds(Arrays.asList(1L, 2L, 3L));\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>3、通过 Wrapper 组装查询条件，查询全部记录:\u003C\u002Fp>\n\u003Cpre>\u003Ccode>QueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F 仅查询 id, name 字段\nqueryWrapper.select("id", "name");\n\u002F\u002F where age = 30\nqueryWrapper.eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\nList<User> users = userMapper.selectList(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>4、查询（根据 columnMap 来设置条件）：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 通过 map 来设置查询条件\nMap<String, Object> columnMap = new HashMap<>();\ncolumnMap.put("name", "张三");\ncolumnMap.put("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE name = '张三' AND age = 30\nList<User> users = userMapper.selectByMap(columnMap);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>5、根据 Wrapper 组装查询条件，查询全部记录，并以 map 的形式返回：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>QueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F 仅查询 id, name 字段\nqueryWrapper.select("id", "name");\n\u002F\u002F where age = 30\nqueryWrapper.eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\nList<Map<String,Object>> users = userMapper.selectMaps(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>6、根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>QueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F where age = 30\nqueryWrapper.eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\nList<Object> ids = userMapper.selectObjs(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>7、根据 Wrapper 条件，查询总记录数：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 组装查询条件\nQueryWrapper<User> queryWrapper = new QueryWrapper<>();\nqueryWrapper.eq("name", "张三").eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT COUNT( * ) FROM user WHERE (name = '张三' AND age = 30)\nlong count = userMapper.selectCount(queryWrapper);\n\nSystem.out.println("总记录数：" + count);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch3>Service 层\u003C\u002Fh3>\n\u003Cp>Mybatis Plus 同样也封装了通用的 Service 层 CRUD 操作，并且提供了更丰富的方法。接下来，我们上手看 Service 层的代码结构，如下图：\u003C\u002Fp>\n\u003Cp>\n\u003Cimg src=\"\u002Fupload\u002F167204808139593-dWMf.jpg\" loading=\"lazy\" title=\"定义 Service 层\" alt=\"定义 Service 层\">\u003Cspan class=\"image-caption\">定义 Service 层\u003C\u002Fspan>\n\u003C\u002Fp>\n\u003Cp>先定义 \u003Ccode>UserService\u003C\u002Fcode> 接口 ，让其继承自 \u003Ccode>IService\u003C\u002Fcode>:\u003C\u002Fp>\n\u003Cpre>\u003Ccode>public interface UserService extends IService<User> {\n}\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>再定义实现类 \u003Ccode>UserServiceImpl\u003C\u002Fcode>，让其继承自 \u003Ccode>ServiceImpl\u003C\u002Fcode>, 同时实现 \u003Ccode>UserService\u003C\u002Fcode> 接口，这样就可以让 \u003Ccode>UserService\u003C\u002Fcode> 拥有了基础通用的 CRUD 功能，当然，实际开发中，业务会更加复杂，就需要向 \u003Ccode>IService\u003C\u002Fcode> 接口自定义方法并实现:\u003C\u002Fp>\n\u003Cpre>\u003Ccode>@Service\npublic class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {\n}\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>注入 \u003Ccode>UserService\u003C\u002Fcode> :\u003C\u002Fp>\n\u003Cpre>\u003Ccode>@Autowired\nprivate UserService userService;\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>Service 层封装的查询方法注意分为 4 块：\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Ccode>getXXX\u003C\u002Fcode> : get 开头的方法；\u003C\u002Fli>\n\u003Cli>\u003Ccode>listXXX\u003C\u002Fcode> : list 开头的方法，用于查询多条数据；\u003C\u002Fli>\n\u003Cli>\u003Ccode>pageXXX\u003C\u002Fcode> : page 开头的方法，用于分页查询；\u003C\u002Fli>\n\u003Cli>\u003Ccode>count\u003C\u002Fcode> : 用于查询总记录数；\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>接下来，我们一一讲解。\u003C\u002Fp>\n\u003Ch4>get 相关方法\u003C\u002Fh4>\n\u003Cp>\u003Ccode>get\u003C\u002Fcode>  开头的相关方法用于查询一条记录，方法如下：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 根据 ID 查询\nT getById(Serializable id);\n\u002F\u002F 根据 Wrapper，查询一条记录。如果结果集是多个会抛出异常\nT getOne(Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper，查询一条记录\nT getOne(Wrapper<T> queryWrapper, boolean throwEx);\n\u002F\u002F 根据 Wrapper，查询一条记录，以 map 的形式返回数据\nMap<String, Object> getMap(Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper，查询一条记录\n<V> V getObj(Wrapper<T> queryWrapper, Function<? super Object, V> mapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Serializable\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>id\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 \u003Ccode>ID\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类 \u003Ccode>QueryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>boolean\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>throwEx\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">有多个 result 是否抛出异常\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>T\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>entity\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Function<? super Object, V>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>mapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">转换函数\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch5>示例代码\u003C\u002Fh5>\n\u003Cp>这里挑两个具有代表性的方法：\u003C\u002Fp>\n\u003Col>\n\u003Cli>根据 ID 查询\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cpre>\u003Ccode>\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id=1        \nUser user = userService.getById(1L);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Col start=\"2\">\n\u003Cli>根据 Wrapper，查询一条记录。如果结果集是多个会抛出异常：\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cpre>\u003Ccode>\u002F\u002F 组装查询条件\nQueryWrapper<User> queryWrapper = new QueryWrapper<>();\nqueryWrapper.eq("id", 1L).eq("name", "张三");\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (id = 1 AND name = '张三')\nUser user = userService.getOne(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch4>list 相关方法\u003C\u002Fh4>\n\u003Cp>\u003Ccode>list\u003C\u002Fcode>  开头的相关方法用于查询多条记录，方法如下：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 查询所有\nList<T> list();\n\u002F\u002F 查询列表\nList<T> list(Wrapper<T> queryWrapper);\n\u002F\u002F 查询（根据ID 批量查询）\nCollection<T> listByIds(Collection<? extends Serializable> idList);\n\u002F\u002F 查询（根据 columnMap 条件）\nCollection<T> listByMap(Map<String, Object> columnMap);\n\u002F\u002F 查询所有列表, 以 map 的形式返回\nList<Map<String, Object>> listMaps();\n\u002F\u002F 查询列表\nList<Map<String, Object>> listMaps(Wrapper<T> queryWrapper);\n\u002F\u002F 查询全部记录\nList<Object> listObjs();\n\u002F\u002F 查询全部记录\n<V> List<V> listObjs(Function<? super Object, V> mapper);\n\u002F\u002F 根据 Wrapper 条件，查询全部记录\nList<Object> listObjs(Wrapper<T> queryWrapper);\n\u002F\u002F 根据 Wrapper 条件，查询全部记录\n<V> List<V> listObjs(Wrapper<T> queryWrapper, Function<? super Object, V> mapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类 \u003Ccode>QueryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Collection<? extends Serializable>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>idList\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 \u003Ccode>ID\u003C\u002Fcode> 列表\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Map<String, Object>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>columnMap\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">表字段 \u003Ccode>map\u003C\u002Fcode> 对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Function<? super Object, V>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>mapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">转换函数\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch5>示例代码\u003C\u002Fh5>\n\u003Cp>这里挑几个具有代表性的方法：\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 组装查询条件\nQueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F where name = '张三' and age >= 20\nqueryWrapper.eq("name", "张三").ge("age", 20);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (name = '张三' AND age >= 20)\nList<User> users = userService.list(queryWrapper);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cpre>\u003Ccode>\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id IN ( 1 , 2 , 3 )\nList<User> users = userService.listByIds(Arrays.asList(1L, 2L, 3L));\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Cpre>\u003Ccode>Map<String , Object> columnMap = new HashMap<>();\ncolumnMap.put("name", "张三");\ncolumnMap.put("age", 30L);\n\n\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE name = '张三' AND age = 30\nList<User> users = userService.listByMap(columnMap);\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch4>page 分页相关方法\u003C\u002Fh4>\n\u003Cp>放到后面《分页查询》\u003Cspan>\u003Csvg xmlns=\"http:\u002F\u002Fwww.w3.org\u002F2000\u002Fsvg\" style=\"color: #aaa; margin-left: 3px;\" aria-hidden=\"true\" focusable=\"false\" x=\"0px\" y=\"0px\" viewBox=\"0 0 100 100\" width=\"15\" height=\"15\" class=\"icon outbound\">\u003Cpath fill=\"currentColor\" d=\"M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z\">\u003C\u002Fpath> \u003Cpolygon fill=\"currentColor\" points=\"45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9\">\u003C\u002Fpolygon>\u003C\u002Fsvg> \u003Cspan class=\"sr-only\">\u003C\u002Fspan>\u003C\u002Fspan>小节统一讲解；\u003C\u002Fp>\n\u003Ch4>count 查询总记录数\u003C\u002Fh4>\n\u003Cp>查询总记录数 \u003Ccode>count\u003C\u002Fcode> 相关方法如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cimg src=\"\u002Fupload\u002F167248996956072-csmW.jpg\" loading=\"lazy\">\n\u003C\u002Fp>\n\u003Cpre>\u003Ccode>\u002F\u002F 查询总记录数（不带查询条件）\ncount();\n\u002F\u002F 查询总记录数（可以带查询条件）\ncount(Wrapper<T>)\n\u003C\u002Fcode>\u003C\u002Fpre>\n\u003Ch5>示例代码\u003C\u002Fh5>\n\u003Cpre>\u003Ccode>\u002F\u002F 组装查询条件\nQueryWrapper<User> queryWrapper = new QueryWrapper<>();\n\u002F\u002F where age = 30\nqueryWrapper.eq("age", 30);\n\n\u002F\u002F 实际执行 SQL : SELECT COUNT( * ) FROM user WHERE (age = 30)\nlong count = userService.count(queryWrapper);\nSystem.out.println("总记录数：" + count);\n\u003C\u002Fcode>\u003C\u002Fpre>\n13:T103a5,\u003Cp>大家好。\u003C\u002Fp>\n\u003Cp>本小节中，我们将学习如何通过 Mybatis Plus 查询数据库表中的数据。\u003C\u002Fp>\n\u003Ch2 id=\"toc-0\">表结构\u003C\u002Fh2>\n\u003Cp>在前面小节中，我们已经定义好了一个用于测试的用户表， 执行脚本如下：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"DROP%20TABLE%20IF%20EXISTS%20user%3B%0A%0ACREATE%20TABLE%20%60user%60%20(%0A%20%20%60id%60%20bigint(20)%20UNSIGNED%20NOT%20NULL%20AUTO_INCREMENT%20COMMENT%20'%E4%B8%BB%E9%94%AEID'%2C%0A%20%20%60name%60%20varchar(30)%20NOT%20NULL%20DEFAULT%20''%20COMMENT%20'%E5%A7%93%E5%90%8D'%2C%0A%20%20%60age%60%20int(11)%20NULL%20DEFAULT%20NULL%20COMMENT%20'%E5%B9%B4%E9%BE%84'%2C%0A%20%20%60gender%60%20tinyint(2)%20NOT%20NULL%20DEFAULT%200%20COMMENT%20'%E6%80%A7%E5%88%AB%EF%BC%8C0%EF%BC%9A%E5%A5%B3%201%EF%BC%9A%E7%94%B7'%2C%0A%20%20PRIMARY%20KEY%20(%60id%60)%0A)%20COMMENT%20%3D%20'%E7%94%A8%E6%88%B7%E8%A1%A8'%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token keyword\">DROP\u003C\u002Fspan> \u003Cspan class=\"token keyword\">TABLE\u003C\u002Fspan> \u003Cspan class=\"token keyword\">IF\u003C\u002Fspan> \u003Cspan class=\"token keyword\">EXISTS\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token keyword\">CREATE\u003C\u002Fspan> \u003Cspan class=\"token keyword\">TABLE\u003C\u002Fspan> \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>user\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\n  \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>id\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">bigint\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">20\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token keyword\">UNSIGNED\u003C\u002Fspan> \u003Cspan class=\"token operator\">NOT\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">AUTO_INCREMENT\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token string\">'主键ID'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>\n  \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>name\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">varchar\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token operator\">NOT\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">DEFAULT\u003C\u002Fspan> \u003Cspan class=\"token string\">''\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token string\">'姓名'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>\n  \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>age\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">int\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">11\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">DEFAULT\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token string\">'年龄'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>\n  \u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>gender\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">tinyint\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">2\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token operator\">NOT\u003C\u002Fspan> \u003Cspan class=\"token boolean\">NULL\u003C\u002Fspan> \u003Cspan class=\"token keyword\">DEFAULT\u003C\u002Fspan> \u003Cspan class=\"token number\">0\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token string\">'性别，0：女 1：男'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>\n  \u003Cspan class=\"token keyword\">PRIMARY\u003C\u002Fspan> \u003Cspan class=\"token keyword\">KEY\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token identifier\">\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>id\u003Cspan class=\"token punctuation\">`\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan> \u003Cspan class=\"token keyword\">COMMENT\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> \u003Cspan class=\"token string\">'用户表'\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Ch2 id=\"toc-1\">定义实体类\u003C\u002Fh2>\n\u003Cp>定义一个名为 \u003Ccode>User\u003C\u002Fcode> 实体类：\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%40TableName(%22user%22)%0Apublic%20class%20User%20%7B%0A%20%20%20%20%2F**%0A%20%20%20%20%20*%20%E4%B8%BB%E9%94%AE%20ID%2C%20%40TableId%20%E6%B3%A8%E8%A7%A3%E5%AE%9A%E4%B9%89%E5%AD%97%E6%AE%B5%E4%B8%BA%E8%A1%A8%E7%9A%84%E4%B8%BB%E9%94%AE%EF%BC%8Ctype%20%E8%A1%A8%E7%A4%BA%E4%B8%BB%E9%94%AE%E7%B1%BB%E5%9E%8B%EF%BC%8CIdType.AUTO%20%E8%A1%A8%E7%A4%BA%E9%9A%8F%E7%9D%80%E6%95%B0%E6%8D%AE%E5%BA%93%20ID%20%E8%87%AA%E5%A2%9E%0A%20%20%20%20%20*%2F%0A%20%20%20%20%40TableId(type%20%3D%20IdType.AUTO)%0A%20%20%20%20private%20Long%20id%3B%0A%20%20%20%20%2F**%0A%20%20%20%20%20*%20%E5%A7%93%E5%90%8D%0A%20%20%20%20%20*%2F%0A%20%20%20%20private%20String%20name%3B%0A%20%20%20%20%2F**%0A%20%20%20%20%20*%20%E5%B9%B4%E9%BE%84%0A%20%20%20%20%20*%2F%0A%20%20%20%20private%20Integer%20age%3B%0A%20%20%20%20%2F**%0A%20%20%20%20%20*%20%E6%80%A7%E5%88%AB%0A%20%20%20%20%20*%2F%0A%20%20%20%20private%20Integer%20gender%3B%0A%7D%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token annotation punctuation\">@TableName\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"user\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">public\u003C\u002Fspan> \u003Cspan class=\"token keyword\">class\u003C\u002Fspan> \u003Cspan class=\"token class-name\">User\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">{\u003C\u002Fspan>\n    \u003Cspan class=\"token comment\">\u002F**\n     * 主键 ID, @TableId 注解定义字段为表的主键，type 表示主键类型，IdType.AUTO 表示随着数据库 ID 自增\n     *\u002F\u003C\u002Fspan>\n    \u003Cspan class=\"token annotation punctuation\">@TableId\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>type \u003Cspan class=\"token operator\">=\u003C\u002Fspan> \u003Cspan class=\"token class-name\">IdType\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token constant\">AUTO\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\n    \u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Long\u003C\u002Fspan> id\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n    \u003Cspan class=\"token comment\">\u002F**\n     * 姓名\n     *\u002F\u003C\u002Fspan>\n    \u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">String\u003C\u002Fspan> name\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n    \u003Cspan class=\"token comment\">\u002F**\n     * 年龄\n     *\u002F\u003C\u002Fspan>\n    \u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Integer\u003C\u002Fspan> age\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n    \u003Cspan class=\"token comment\">\u002F**\n     * 性别\n     *\u002F\u003C\u002Fspan>\n    \u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Integer\u003C\u002Fspan> gender\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">}\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>不明白 Mybatis Plus 实体类注解的小伙伴，可参考前面小节\u003Cspan>\u003Csvg xmlns=\"http:\u002F\u002Fwww.w3.org\u002F2000\u002Fsvg\" style=\"color: #aaa; margin-left: 3px;\" aria-hidden=\"true\" focusable=\"false\" x=\"0px\" y=\"0px\" viewBox=\"0 0 100 100\" width=\"15\" height=\"15\" class=\"icon outbound\">\u003Cpath fill=\"currentColor\" d=\"M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z\">\u003C\u002Fpath> \u003Cpolygon fill=\"currentColor\" points=\"45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9\">\u003C\u002Fpolygon>\u003C\u002Fsvg> \u003Cspan class=\"sr-only\">\u003C\u002Fspan>\u003C\u002Fspan>, 有详细解释。\u003C\u002Fp>\n\u003Ch2 id=\"toc-2\">开始查询数据\u003C\u002Fh2>\n\u003Cp>Mybatis Plus 对 Mapper 层和 Service 层都将常见的增删改查操作封装好了，只需简单的继承，即可轻松搞定对数据的增删改查，本文重点讲解查询相关的部分。\u003C\u002Fp>\n\u003Ch3 id=\"toc-3\">Mapper 层\u003C\u002Fh3>\n\u003Cp>定义一个 \u003Ccode>UserMapper\u003C\u002Fcode> , 让其继承自 \u003Ccode>BaseMapper\u003C\u002Fcode> :\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"public%20interface%20UserMapper%20extends%20BaseMapper%3CUser%3E%20%7B%0A%7D%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token keyword\">public\u003C\u002Fspan> \u003Cspan class=\"token keyword\">interface\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserMapper\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">BaseMapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">User\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">{\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">}\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>然后，注入 Mapper :\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%40Autowired%0Aprivate%20UserMapper%20userMapper%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token annotation punctuation\">@Autowired\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserMapper\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>\u003Ccode>BaseMapper\u003C\u002Fcode> 提供的查询相关的方法如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cdiv class=\"img-loading\">\u003Cimg src=\"\u002Fupload\u002F167238066532413-dlWV.jpg\" loading=\"lazy\">\u003C\u002Fdiv>\n\u003C\u002Fp>\n\u003Cp>解释一下每个方法的作用：\u003C\u002Fp>\n\u003Cdiv class=\"language-javascript\" data-ext=\"javascript\" data-code=\"%2F%2F%20%E6%A0%B9%E6%8D%AE%20ID%20%E6%9F%A5%E8%AF%A2%0AT%20selectById(Serializable%20id)%3B%0A%2F%2F%20%E9%80%9A%E8%BF%87%20Wrapper%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%0AT%20selectOne(Wrapper%3CT%3E%20queryWrapper)%3B%0A%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%EF%BC%88%E6%A0%B9%E6%8D%AEID%20%E6%89%B9%E9%87%8F%E6%9F%A5%E8%AF%A2%EF%BC%89%0AList%3CT%3E%20selectBatchIds(Collection%3C%3F%20extends%20Serializable%3E%20idList)%3B%0A%2F%2F%20%E9%80%9A%E8%BF%87%20Wrapper%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0AList%3CT%3E%20selectList(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%EF%BC%88%E6%A0%B9%E6%8D%AE%20columnMap%20%E6%9D%A5%E8%AE%BE%E7%BD%AE%E6%9D%A1%E4%BB%B6%EF%BC%89%0AList%3CT%3E%20selectByMap(Map%3CString%2C%20Object%3E%20columnMap)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%EF%BC%8C%E5%B9%B6%E4%BB%A5%20map%20%E7%9A%84%E5%BD%A2%E5%BC%8F%E8%BF%94%E5%9B%9E%0AList%3CMap%3CString%2C%20Object%3E%3E%20selectMaps(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%E3%80%82%E6%B3%A8%E6%84%8F%EF%BC%9A%20%E5%8F%AA%E8%BF%94%E5%9B%9E%E7%AC%AC%E4%B8%80%E4%B8%AA%E5%AD%97%E6%AE%B5%E7%9A%84%E5%80%BC%0AList%3CObject%3E%20selectObjs(Wrapper%3CT%3E%20queryWrapper)%3B%0A%0A%2F%2F%20%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%20%E5%88%86%E9%A1%B5%E7%9B%B8%E5%85%B3%20%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%3D%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20entity%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%EF%BC%88%E5%B9%B6%E7%BF%BB%E9%A1%B5%EF%BC%89%0AIPage%3CT%3E%20selectPage(IPage%3CT%3E%20page%2C%20Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%EF%BC%88%E5%B9%B6%E7%BF%BB%E9%A1%B5%EF%BC%89%0AIPage%3CMap%3CString%2C%20Object%3E%3E%20selectMapsPage(IPage%3CT%3E%20page%2C%20Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E6%80%BB%E8%AE%B0%E5%BD%95%E6%95%B0%0AInteger%20selectCount(Wrapper%3CT%3E%20queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-javascript\">\u003Cspan class=\"token comment\">\u002F\u002F 根据 ID 查询\u003C\u002Fspan>\n\u003Cspan class=\"token constant\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">selectById\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Serializable id\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 通过 Wrapper 组装查询条件，查询一条记录\u003C\u002Fspan>\n\u003Cspan class=\"token constant\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">selectOne\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 查询（根据ID 批量查询）\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectBatchIds\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Collection\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Serializable\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> idList\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 通过 Wrapper 组装查询条件，查询全部记录\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectList\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询（根据 columnMap 来设置条件）\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectByMap\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> columnMap\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 组装查询条件，查询全部记录，并以 map 的形式返回\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectMaps\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F =========================== 分页相关 ===========================\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 entity 条件，查询全部记录（并翻页）\u003C\u002Fspan>\nIPage\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectPage\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>IPage\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> page\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询全部记录（并翻页）\u003C\u002Fspan>\nIPage\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> \u003Cspan class=\"token function\">selectMapsPage\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>IPage\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> page\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询总记录数\u003C\u002Fspan>\nInteger \u003Cspan class=\"token function\">selectCount\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Serializable\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>id\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 ID\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类（可以为 null）\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Collection<? extends Serializable>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>idList\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 ID 列表(不能为 null 以及 empty)\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Map<String, Object>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>columnMap\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">表字段 map 对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>IPage<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>page\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">分页查询条件（可以为 RowBounds.DEFAULT）\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch4 id=\"toc-4\">示例代码\u003C\u002Fh4>\n\u003Cp>接下来，本文来演示一些示例代码以便你快速了解如何使用，注意，分页相关的方法暂不做讲解，后面会单独开一篇来详细讲解。\u003C\u002Fp>\n\u003Cp>1、根据 ID 查询：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20id%3D1%20%0AUser%20user%20%3D%20userMapper.selectById(1L)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id=1 \u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">User\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectById\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>2、通过 Wrapper 组装查询条件，查询一条记录:\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"QueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20%E4%BB%85%E6%9F%A5%E8%AF%A2%20id%2C%20name%20%E5%AD%97%E6%AE%B5%0AqueryWrapper.select(%22id%22%2C%20%22name%22)%3B%0A%2F%2F%20where%20id%20%3D%201%0AqueryWrapper.eq(%22id%22%2C%201L)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20(id%20%3D%201)%0AUser%20user%20%3D%20userMapper.selectOne(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">QueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 仅查询 id, name 字段\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token keyword\">select\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where id = 1\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (id = 1)\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">User\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectOne\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cblockquote>\n\u003Cp>注意： \u003Ccode>selectOne\u003C\u002Fcode> 方法期望仅返回一条数据，若实际查询到多条数据，会主动抛出异常，内部源码如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cdiv class=\"img-loading\">\u003Cimg src=\"\u002Fupload\u002F167238290868316-figO.jpg\" loading=\"lazy\">\u003C\u002Fdiv>\n\u003C\u002Fp>\n\u003C\u002Fblockquote>\n\u003Cp>2、查询（根据ID 批量查询）：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20id%20IN%20(%201%20%2C%202%20%2C%203%20)%0AList%3CUser%3E%20users%20%3D%20userMapper.selectBatchIds(Arrays.asList(1L%2C%202L%2C%203L))%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id IN ( 1 , 2 , 3 )\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectBatchIds\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Arrays\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>asList\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">2\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">3\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>3、通过 Wrapper 组装查询条件，查询全部记录:\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"QueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20%E4%BB%85%E6%9F%A5%E8%AF%A2%20id%2C%20name%20%E5%AD%97%E6%AE%B5%0AqueryWrapper.select(%22id%22%2C%20%22name%22)%3B%0A%2F%2F%20where%20age%20%3D%2030%0AqueryWrapper.eq(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%20FROM%20user%20WHERE%20(age%20%3D%2030)%0AList%3CUser%3E%20users%20%3D%20userMapper.selectList(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">QueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 仅查询 id, name 字段\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token keyword\">select\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where age = 30\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectList\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>4、查询（根据 columnMap 来设置条件）：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E9%80%9A%E8%BF%87%20map%20%E6%9D%A5%E8%AE%BE%E7%BD%AE%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%0AMap%3CString%2C%20Object%3E%20columnMap%20%3D%20new%20HashMap%3C%3E()%3B%0AcolumnMap.put(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22)%3B%0AcolumnMap.put(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20name%20%3D%20'%E5%BC%A0%E4%B8%89'%20AND%20age%20%3D%2030%0AList%3CUser%3E%20users%20%3D%20userMapper.selectByMap(columnMap)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 通过 map 来设置查询条件\u003C\u002Fspan>\nMap\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> columnMap \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new HashMap\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\ncolumnMap\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>put\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\ncolumnMap\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>put\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE name = '张三' AND age = 30\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectByMap\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>columnMap\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>5、根据 Wrapper 组装查询条件，查询全部记录，并以 map 的形式返回：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"QueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20%E4%BB%85%E6%9F%A5%E8%AF%A2%20id%2C%20name%20%E5%AD%97%E6%AE%B5%0AqueryWrapper.select(%22id%22%2C%20%22name%22)%3B%0A%2F%2F%20where%20age%20%3D%2030%0AqueryWrapper.eq(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%20FROM%20user%20WHERE%20(age%20%3D%2030)%0AList%3CMap%3CString%2CObject%3E%3E%20users%20%3D%20userMapper.selectMaps(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">QueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 仅查询 id, name 字段\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token keyword\">select\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where age = 30\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectMaps\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>6、根据 Wrapper 条件，查询全部记录。注意： 只返回第一个字段的值：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"QueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20where%20age%20%3D%2030%0AqueryWrapper.eq(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%20FROM%20user%20WHERE%20(age%20%3D%2030)%0AList%3CObject%3E%20ids%20%3D%20userMapper.selectObjs(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">QueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where age = 30\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name FROM user WHERE (age = 30)\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> ids \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectObjs\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>7、根据 Wrapper 条件，查询总记录数：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%0AQueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0AqueryWrapper.eq(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22).eq(%22age%22%2C%2030)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20COUNT(%20*%20)%20FROM%20user%20WHERE%20(name%20%3D%20'%E5%BC%A0%E4%B8%89'%20AND%20age%20%3D%2030)%0Along%20count%20%3D%20userMapper.selectCount(queryWrapper)%3B%0A%0ASystem.out.println(%22%E6%80%BB%E8%AE%B0%E5%BD%95%E6%95%B0%EF%BC%9A%22%20%2B%20count)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 组装查询条件\u003C\u002Fspan>\nQueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT COUNT( * ) FROM user WHERE (name = '张三' AND age = 30)\u003C\u002Fspan>\nlong count \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userMapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>selectCount\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\nSystem\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>\u003Cspan class=\"token keyword\">out\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>println\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"总记录数：\"\u003C\u002Fspan> \u003Cspan class=\"token operator\">+\u003C\u002Fspan> count\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Ch3 id=\"toc-5\">Service 层\u003C\u002Fh3>\n\u003Cp>Mybatis Plus 同样也封装了通用的 Service 层 CRUD 操作，并且提供了更丰富的方法。接下来，我们上手看 Service 层的代码结构，如下图：\u003C\u002Fp>\n\u003Cp>\n\u003Cdiv class=\"img-loading\">\u003Cimg src=\"\u002Fupload\u002F167204808139593-dWMf.jpg\" loading=\"lazy\" title=\"定义 Service 层\" alt=\"定义 Service 层\">\u003C\u002Fdiv>\u003Cspan class=\"image-caption\">定义 Service 层\u003C\u002Fspan>\n\u003C\u002Fp>\n\u003Cp>先定义 \u003Ccode>UserService\u003C\u002Fcode> 接口 ，让其继承自 \u003Ccode>IService\u003C\u002Fcode>:\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"public%20interface%20UserService%20extends%20IService%3CUser%3E%20%7B%0A%7D%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token keyword\">public\u003C\u002Fspan> \u003Cspan class=\"token keyword\">interface\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserService\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">IService\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">User\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">{\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">}\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>再定义实现类 \u003Ccode>UserServiceImpl\u003C\u002Fcode>，让其继承自 \u003Ccode>ServiceImpl\u003C\u002Fcode>, 同时实现 \u003Ccode>UserService\u003C\u002Fcode> 接口，这样就可以让 \u003Ccode>UserService\u003C\u002Fcode> 拥有了基础通用的 CRUD 功能，当然，实际开发中，业务会更加复杂，就需要向 \u003Ccode>IService\u003C\u002Fcode> 接口自定义方法并实现:\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%40Service%0Apublic%20class%20UserServiceImpl%20extends%20ServiceImpl%3CUserMapper%2C%20User%3E%20implements%20UserService%20%7B%0A%7D%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token annotation punctuation\">@Service\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">public\u003C\u002Fspan> \u003Cspan class=\"token keyword\">class\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserServiceImpl\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">ServiceImpl\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">UserMapper\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token class-name\">User\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token keyword\">implements\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserService\u003C\u002Fspan> \u003Cspan class=\"token punctuation\">{\u003C\u002Fspan>\n\u003Cspan class=\"token punctuation\">}\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>注入 \u003Ccode>UserService\u003C\u002Fcode> :\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%40Autowired%0Aprivate%20UserService%20userService%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token annotation punctuation\">@Autowired\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">private\u003C\u002Fspan> \u003Cspan class=\"token class-name\">UserService\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>Service 层封装的查询方法注意分为 4 块：\u003C\u002Fp>\n\u003Cul>\n\u003Cli>\u003Ccode>getXXX\u003C\u002Fcode> : get 开头的方法；\u003C\u002Fli>\n\u003Cli>\u003Ccode>listXXX\u003C\u002Fcode> : list 开头的方法，用于查询多条数据；\u003C\u002Fli>\n\u003Cli>\u003Ccode>pageXXX\u003C\u002Fcode> : page 开头的方法，用于分页查询；\u003C\u002Fli>\n\u003Cli>\u003Ccode>count\u003C\u002Fcode> : 用于查询总记录数；\u003C\u002Fli>\n\u003C\u002Ful>\n\u003Cp>接下来，我们一一讲解。\u003C\u002Fp>\n\u003Ch4 id=\"toc-6\">get 相关方法\u003C\u002Fh4>\n\u003Cp>\u003Ccode>get\u003C\u002Fcode>  开头的相关方法用于查询一条记录，方法如下：\u003C\u002Fp>\n\u003Cdiv class=\"language-java\" data-ext=\"java\" data-code=\"%2F%2F%20%E6%A0%B9%E6%8D%AE%20ID%20%E6%9F%A5%E8%AF%A2%0AT%20getById(Serializable%20id)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%E3%80%82%E5%A6%82%E6%9E%9C%E7%BB%93%E6%9E%9C%E9%9B%86%E6%98%AF%E5%A4%9A%E4%B8%AA%E4%BC%9A%E6%8A%9B%E5%87%BA%E5%BC%82%E5%B8%B8%0AT%20getOne(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%0AT%20getOne(Wrapper%3CT%3E%20queryWrapper%2C%20boolean%20throwEx)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%EF%BC%8C%E4%BB%A5%20map%20%E7%9A%84%E5%BD%A2%E5%BC%8F%E8%BF%94%E5%9B%9E%E6%95%B0%E6%8D%AE%0AMap%3CString%2C%20Object%3E%20getMap(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%EF%BC%8C%E6%9F%A5%E8%AF%A2%E4%B8%80%E6%9D%A1%E8%AE%B0%E5%BD%95%0A%3CV%3E%20V%20getObj(Wrapper%3CT%3E%20queryWrapper%2C%20Function%3C%3F%20super%20Object%2C%20V%3E%20mapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-java\">\u003Cspan class=\"token comment\">\u002F\u002F 根据 ID 查询\u003C\u002Fspan>\n\u003Cspan class=\"token class-name\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">getById\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Serializable\u003C\u002Fspan> id\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper，查询一条记录。如果结果集是多个会抛出异常\u003C\u002Fspan>\n\u003Cspan class=\"token class-name\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">getOne\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Wrapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">T\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper，查询一条记录\u003C\u002Fspan>\n\u003Cspan class=\"token class-name\">T\u003C\u002Fspan> \u003Cspan class=\"token function\">getOne\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Wrapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">T\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token keyword\">boolean\u003C\u002Fspan> throwEx\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper，查询一条记录，以 map 的形式返回数据\u003C\u002Fspan>\n\u003Cspan class=\"token class-name\">Map\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">String\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Object\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token function\">getMap\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Wrapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">T\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper，查询一条记录\u003C\u002Fspan>\n\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">V\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> \u003Cspan class=\"token class-name\">V\u003C\u002Fspan> \u003Cspan class=\"token function\">getObj\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token class-name\">Wrapper\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token class-name\">T\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Function\u003C\u002Fspan>\u003Cspan class=\"token generics\">\u003Cspan class=\"token punctuation\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">super\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Object\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token class-name\">V\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">>\u003C\u002Fspan>\u003C\u002Fspan> mapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Serializable\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>id\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 \u003Ccode>ID\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类 \u003Ccode>QueryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>boolean\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>throwEx\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">有多个 result 是否抛出异常\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>T\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>entity\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Function<? super Object, V>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>mapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">转换函数\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch5 id=\"toc-7\">示例代码\u003C\u002Fh5>\n\u003Cp>这里挑两个具有代表性的方法：\u003C\u002Fp>\n\u003Col>\n\u003Cli>根据 ID 查询\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20id%3D1%20%20%20%20%20%20%20%20%0AUser%20user%20%3D%20userService.getById(1L)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id=1        \u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">User\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>getById\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Col start=\"2\">\n\u003Cli>根据 Wrapper，查询一条记录。如果结果集是多个会抛出异常：\u003C\u002Fli>\n\u003C\u002Fol>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%0AQueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0AqueryWrapper.eq(%22id%22%2C%201L).eq(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20(id%20%3D%201%20AND%20name%20%3D%20'%E5%BC%A0%E4%B8%89')%0AUser%20user%20%3D%20userService.getOne(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 组装查询条件\u003C\u002Fspan>\nQueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"id\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (id = 1 AND name = '张三')\u003C\u002Fspan>\n\u003Cspan class=\"token keyword\">User\u003C\u002Fspan> \u003Cspan class=\"token keyword\">user\u003C\u002Fspan> \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>getOne\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Ch4 id=\"toc-8\">list 相关方法\u003C\u002Fh4>\n\u003Cp>\u003Ccode>list\u003C\u002Fcode>  开头的相关方法用于查询多条记录，方法如下：\u003C\u002Fp>\n\u003Cdiv class=\"language-javascript\" data-ext=\"javascript\" data-code=\"%2F%2F%20%E6%9F%A5%E8%AF%A2%E6%89%80%E6%9C%89%0AList%3CT%3E%20list()%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E5%88%97%E8%A1%A8%0AList%3CT%3E%20list(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%EF%BC%88%E6%A0%B9%E6%8D%AEID%20%E6%89%B9%E9%87%8F%E6%9F%A5%E8%AF%A2%EF%BC%89%0ACollection%3CT%3E%20listByIds(Collection%3C%3F%20extends%20Serializable%3E%20idList)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%EF%BC%88%E6%A0%B9%E6%8D%AE%20columnMap%20%E6%9D%A1%E4%BB%B6%EF%BC%89%0ACollection%3CT%3E%20listByMap(Map%3CString%2C%20Object%3E%20columnMap)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E6%89%80%E6%9C%89%E5%88%97%E8%A1%A8%2C%20%E4%BB%A5%20map%20%E7%9A%84%E5%BD%A2%E5%BC%8F%E8%BF%94%E5%9B%9E%0AList%3CMap%3CString%2C%20Object%3E%3E%20listMaps()%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E5%88%97%E8%A1%A8%0AList%3CMap%3CString%2C%20Object%3E%3E%20listMaps(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0AList%3CObject%3E%20listObjs()%3B%0A%2F%2F%20%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0A%3CV%3E%20List%3CV%3E%20listObjs(Function%3C%3F%20super%20Object%2C%20V%3E%20mapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0AList%3CObject%3E%20listObjs(Wrapper%3CT%3E%20queryWrapper)%3B%0A%2F%2F%20%E6%A0%B9%E6%8D%AE%20Wrapper%20%E6%9D%A1%E4%BB%B6%EF%BC%8C%E6%9F%A5%E8%AF%A2%E5%85%A8%E9%83%A8%E8%AE%B0%E5%BD%95%0A%3CV%3E%20List%3CV%3E%20listObjs(Wrapper%3CT%3E%20queryWrapper%2C%20Function%3C%3F%20super%20Object%2C%20V%3E%20mapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-javascript\">\u003Cspan class=\"token comment\">\u002F\u002F 查询所有\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">list\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询列表\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">list\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询（根据ID 批量查询）\u003C\u002Fspan>\nCollection\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listByIds\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Collection\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">extends\u003C\u002Fspan> \u003Cspan class=\"token class-name\">Serializable\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> idList\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询（根据 columnMap 条件）\u003C\u002Fspan>\nCollection\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listByMap\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> columnMap\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询所有列表, 以 map 的形式返回\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> \u003Cspan class=\"token function\">listMaps\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询列表\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>>\u003C\u002Fspan> \u003Cspan class=\"token function\">listMaps\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询全部记录\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 查询全部记录\u003C\u002Fspan>\n\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> List\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Function\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">super\u003C\u002Fspan> Object\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> mapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询全部记录\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F 根据 Wrapper 条件，查询全部记录\u003C\u002Fspan>\n\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> List\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> \u003Cspan class=\"token function\">listObjs\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Wrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token constant\">T\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Function\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token operator\">?\u003C\u002Fspan> \u003Cspan class=\"token keyword\">super\u003C\u002Fspan> Object\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token constant\">V\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> mapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cp>参数说明：\u003C\u002Fp>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth align=\"center\">类型\u003C\u002Fth>\n\u003Cth align=\"center\">参数名\u003C\u002Fth>\n\u003Cth align=\"center\">描述\u003C\u002Fth>\n\u003C\u002Ftr>\n\u003C\u002Fthead>\n\u003Ctbody>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Wrapper<T>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>queryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">实体对象封装操作类 \u003Ccode>QueryWrapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Collection<? extends Serializable>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>idList\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">主键 \u003Ccode>ID\u003C\u002Fcode> 列表\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Map<String, Object>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>columnMap\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">表字段 \u003Ccode>map\u003C\u002Fcode> 对象\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003Ctr>\n\u003Ctd align=\"center\">\u003Ccode>Function<? super Object, V>\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">\u003Ccode>mapper\u003C\u002Fcode>\u003C\u002Ftd>\n\u003Ctd align=\"center\">转换函数\u003C\u002Ftd>\n\u003C\u002Ftr>\n\u003C\u002Ftbody>\n\u003C\u002Ftable>\n\u003Ch5 id=\"toc-9\">示例代码\u003C\u002Fh5>\n\u003Cp>这里挑几个具有代表性的方法：\u003C\u002Fp>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E7%BB%84%E8%A3%85%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%0AQueryWrapper%3CUser%3E%20queryWrapper%20%3D%20new%20QueryWrapper%3C%3E()%3B%0A%2F%2F%20where%20name%20%3D%20'%E5%BC%A0%E4%B8%89'%20and%20age%20%3E%3D%2020%0AqueryWrapper.eq(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22).ge(%22age%22%2C%2020)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20(name%20%3D%20'%E5%BC%A0%E4%B8%89'%20AND%20age%20%3E%3D%2020)%0AList%3CUser%3E%20users%20%3D%20userService.list(queryWrapper)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 组装查询条件\u003C\u002Fspan>\nQueryWrapper\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> queryWrapper \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new QueryWrapper\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003Cspan class=\"token comment\">\u002F\u002F where name = '张三' and age >= 20\u003C\u002Fspan>\nqueryWrapper\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>eq\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>ge\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">20\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE (name = '张三' AND age >= 20)\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>list\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>queryWrapper\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20id%20IN%20(%201%20%2C%202%20%2C%203%20)%0AList%3CUser%3E%20users%20%3D%20userService.listByIds(Arrays.asList(1L%2C%202L%2C%203L))%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE id IN ( 1 , 2 , 3 )\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>listByIds\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>Arrays\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>asList\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token number\">1\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">2\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">3\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Cdiv class=\"language-sql\" data-ext=\"sql\" data-code=\"Map%3CString%20%2C%20Object%3E%20columnMap%20%3D%20new%20HashMap%3C%3E()%3B%0AcolumnMap.put(%22name%22%2C%20%22%E5%BC%A0%E4%B8%89%22)%3B%0AcolumnMap.put(%22age%22%2C%2030L)%3B%0A%0A%2F%2F%20%E5%AE%9E%E9%99%85%E6%89%A7%E8%A1%8C%20SQL%20%3A%20SELECT%20id%2Cname%2Cage%2Cgender%20FROM%20user%20WHERE%20name%20%3D%20'%E5%BC%A0%E4%B8%89'%20AND%20age%20%3D%2030%0AList%3CUser%3E%20users%20%3D%20userService.listByMap(columnMap)%3B%0A\">\n        \u003Cbutton class=\"vp-copy-code-button\" data-copy data-copied=\"已复制\" aria-label=\"复制代码\">\u003C\u002Fbutton>\n        \u003Cpre>\u003Ccode class=\"language-sql\">Map\u003Cspan class=\"token operator\"><\u003C\u002Fspan>String \u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> Object\u003Cspan class=\"token operator\">>\u003C\u002Fspan> columnMap \u003Cspan class=\"token operator\">=\u003C\u002Fspan> new HashMap\u003Cspan class=\"token operator\"><>\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\ncolumnMap\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>put\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"name\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token string\">\"张三\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\ncolumnMap\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>put\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>\u003Cspan class=\"token string\">\"age\"\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">,\u003C\u002Fspan> \u003Cspan class=\"token number\">30\u003C\u002Fspan>L\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\n\u003Cspan class=\"token comment\">\u002F\u002F 实际执行 SQL : SELECT id,name,age,gender FROM user WHERE name = '张三' AND age = 30\u003C\u002Fspan>\nList\u003Cspan class=\"token operator\"><\u003C\u002Fspan>\u003Cspan class=\"token keyword\">User\u003C\u002Fspan>\u003Cspan class=\"token operator\">>\u003C\u002Fspan> users \u003Cspan class=\"token operator\">=\u003C\u002Fspan> userService\u003Cspan class=\"token punctuation\">.\u003C\u002Fspan>listByMap\u003Cspan class=\"token punctuation\">(\u003C\u002Fspan>columnMap\u003Cspan class=\"token punctuation\">)\u003C\u002Fspan>\u003Cspan class=\"token punctuation\">;\u003C\u002Fspan>\n\u003C\u002Fcode>\u003C\u002Fpre>\n      \u003C\u002Fdiv>\n\u003Ch4 id=\"toc-10\">page 分页相关方法\u003C\u002Fh4>\n\u003Cp>放到后面《分页查询》\u003Cspan>\u003Csvg xmlns=\"http:\u002F\u002Fwww.w3.org\u002F2000\u002Fsvg\" style=\"color: #aaa; margin-left: 3px;\" aria-hidden=\"true\" focusable=\"false\" x=\"0px\" y=\"0px\" viewBox=\"0 0 100 100\" width=\"15\" height=\"15\" class=\"icon outbound\">\u003Cpath fill=\"currentColor\" d=\"M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z\">\u003C\u002Fpath> \u003Cpolygon fill=\"currentColor\" points=\"45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9\">\u003C\u002Fpolygon>\u003C\u002Fsvg> \u003Cspan class=\"sr-only\">\u003C\u002Fspan>\u003C\u002Fspan>小节统一讲解；\u003C\u002Fp>\n\u003Ch4 id=\"toc-11\">count 查询总记录数\u003C\u002Fh4>\n\u003Cp>查询总记录数 \u003Ccode>count\u003C\u002Fcode> 相关方法如下：\u003C\u002Fp>\n\u003Cp>\n\u003Cdiv class=\"img-loading\">\u003Cimg src=\"\u002Fupload\u002F167248996956072-csmW.jpg\" loading=\"lazy\">\u003C\u002Fdiv>\n\u003C\u002Fp>"]