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readme
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README-zh.md
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<!--suppress HtmlDeprecatedAttribute -->
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<p align="center">
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<a href="https://github.com/yulichang/mybatis-plus-join" target="_blank">
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<img alt="Mybatis-Plus-Join-Logo" src="https://mybatisplusjoin.com/lg.png">
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</a>
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</p>
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<h1 align="center">MyBatis-Plus-Join</h1>
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<p align="center">
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为简化开发工作、提高生产率而生
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</p>
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<p align="center">
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<a href="https://github.com/yulichang/mybatis-plus-join" target="_blank">
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<img src="https://img.shields.io/github/stars/yulichang/mybatis-plus-join.svg?style=social&label=Stars" alt=""/>
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</a>
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<a href="https://gitee.com/best_handsome/mybatis-plus-join" target="_blank">
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<img src="https://gitee.com/best_handsome/mybatis-plus-join/badge/star.svg?theme=dark" alt=""/>
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</a>
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<br/>
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<a href="https://central.sonatype.com/artifact/com.github.yulichang/mybatis-plus-join-boot-starter">
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<img alt="maven" src="https://img.shields.io/maven-central/v/com.github.yulichang/mybatis-plus-join-boot-starter.svg?style=flat-square">
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</a>
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<a href="https://www.apache.org/licenses/LICENSE-2.0">
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<img alt="code style" src="https://img.shields.io/badge/license-Apache%202-4EB1BA.svg?style=flat-square">
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</a>
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</p>
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<p align="center">
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对 <a href="https://gitee.com/baomidou/mybatis-plus" target="_blank">MyBatis-Plus</a> 多表查询的扩展 |
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<a href="https://gitee.com/best_handsome/mybatis-plus-join-demo" target="_blank">演示工程</a> |
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<a href="https://www.baidu.com/link?url=wdmhssysW-Mj19Gkcc2CBOzNVoimHat57mlnH78SEU_6y0awYgDKTBy7es9BXnAH&wd=&eqid=908484020001866e000000056440b5e3" target="_blank">使用文档</a> |
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点个Star支持一下吧 (☆▽☆)
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</p>
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<p align="center">
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QQ群:1022221898 或者
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<a href="https://gitee.com/best_handsome/mybatis-plus-join/issues/I65N2M" target="_blank">添加作者微信，备注MPJ，加入微信群</a>
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<br/>
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<img width="200px" height="200px" src="https://mybatisplusjoin.com/qr.png" alt="添加作者微信，备注MPJ，加入微信群"/>
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</p>
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### <a href="https://www.baidu.com/link?url=6NtKqbGKUIIdwoBUaqNkQnLiG3d5y03L6Pfg6ODId0VKfPifpB1xqdQzsBprm-0h&wd=&eqid=d26e7f1600004777000000056440ade6" target="_blank">使用文档WIKI</a>
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## 使用方法
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### 安装
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- Maven
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```xml
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<dependency>
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<groupId>com.github.yulichang</groupId>
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<artifactId>mybatis-plus-join-boot-starter</artifactId>
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<version>1.4.7.2</version>
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</dependency>
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```
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- Gradle
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```
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implementation 'com.github.yulichang:mybatis-plus-join-boot-starter:1.4.7.1'
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```
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或者clone代码到本地执行 mvn install, 再引入以上依赖
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<br>
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注意: MyBatis Plus版本需要3.3.0+
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<br>
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### 使用
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* mapper继承MPJBaseMapper (必选)
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* service继承MPJBaseService (可选)
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* serviceImpl继承MPJBaseServiceImpl (可选)
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### Lambda形式用法（MPJLambdaWrapper）
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#### 简单的连表查询
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```java
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class test {
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@Resource
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private UserMapper userMapper;
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void testJoin() {
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//和Mybatis plus一致，MPJLambdaWrapper的泛型必须是主表的泛型，并且要用主表的Mapper来调用
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MPJLambdaWrapper<UserDO> wrapper = JoinWrappers.lambda(UserDO.class)
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.selectAll(UserDO.class)//查询user表全部字段
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.select(UserAddressDO::getTel)//查询user_address tel 字段
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.selectAs(UserAddressDO::getAddress, UserDTO::getUserAddress)//别名
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.select(AreaDO::getProvince, AreaDO::getCity)
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.leftJoin(UserAddressDO.class, UserAddressDO::getUserId, UserDO::getId)
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.leftJoin(AreaDO.class, AreaDO::getId, UserAddressDO::getAreaId)
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.eq(UserDO::getId, 1)
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.like(UserAddressDO::getTel, "1")
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.gt(UserDO::getId, 5);
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//连表查询 返回自定义ResultType
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List<UserDTO> list = userMapper.selectJoinList(UserDTO.class, wrapper);
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//分页查询 （需要启用 mybatis plus 分页插件）
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Page<UserDTO> listPage = userMapper.selectJoinPage(new Page<>(2, 10), UserDTO.class, wrapper);
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}
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}
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```
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对应sql
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```
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SELECT
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t.id, t.name, t.sex, t.head_img,
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t1.tel, t1.address AS userAddress,
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t2.province, t2.city
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FROM
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user t
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LEFT JOIN user_address t1 ON t1.user_id = t.id
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LEFT JOIN area t2 ON t2.id = t1.area_id
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WHERE (
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t.id = ?
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AND t1.tel LIKE ?
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AND t.id > ?)
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```
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说明:
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* UserDTO.class 查询结果返回类(resultType)
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* selectAll() 查询指定实体类的全部字段
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* select() 查询指定的字段,支持可变参数,同一个select只能查询相同表的字段
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* selectAs() 字段别名查询,用于数据库字段与业务实体类属性名不一致时使用
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* leftJoin() 参数说明
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第一个参数: 参与连表的实体类class
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第二个参数: 连表的ON字段,这个属性必须是第一个参数实体类的属性
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第三个参数: 参与连表的ON的另一个实体类属性
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* 默认主表别名是t,其他的表别名以先后调用的顺序使用t1,t2,t3....
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* 条件查询,可以查询主表以及参与连接的所有表的字段,全部调用mp原生的方法,正常使用没有sql注入风险
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#### 一对多查询
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```java
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class test {
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@Resource
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private UserMapper userMapper;
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@Test
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void testResultMap() {
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MPJLambdaWrapper<UserDO> wrapper = new MPJLambdaWrapper<>(User.class)
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.selectAll(UserDO.class)
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//对多查询
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.selectCollection(AddressDO.class, UesrDTO::getAddressList)
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//对一查询
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.selectAssociation(AddressDO.class, UesrDTO::getAddress)
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.leftJoin(AddressDO.class, AddressDO::getUserId, UserDO::getId);
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List<UserDTO> dtoList = userMapper.selectJoinList(UserDTO.class, wrapper);
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//关于对多分页查询
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//由于嵌套结果方式会导致结果集被折叠，因此分页查询的结果在折叠后总数会减少，所以无法保证分页结果数量正确。
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}
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}
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```
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MPJLambdaWrapper其他功能
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* <a href="https://mybatisplusjoin.com/pages/core/lambda/select/selectCollection.html" target="_blank">
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一对一，一对多使用</a>
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* <a href="https://mybatisplusjoin.com/pages/core/lambda/select/selectFunc.html" target="_blank">简单的SQL函数使用</a>
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* <a href="https://mybatisplusjoin.com/pages/core/lambda/join/leftJoin.html" target="_blank">ON语句多条件支持</a>
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* <a href="https://www.baidu.com/link?url=wdmhssysW-Mj19Gkcc2CBOzNVoimHat57mlnH78SEU_6y0awYgDKTBy7es9BXnAH&wd=&eqid=908484020001866e000000056440b5e3" target="_blank">其他全部功能请参考使用文档</a>
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# <a href="https://www.baidu.com/link?url=wdmhssysW-Mj19Gkcc2CBOzNVoimHat57mlnH78SEU_6y0awYgDKTBy7es9BXnAH&wd=&eqid=908484020001866e000000056440b5e3" target="_blank">使用文档 wiki</a>
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@ -34,8 +34,6 @@
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<p align="center">
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QQ群:1022221898 或者
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<a href="https://gitee.com/best_handsome/mybatis-plus-join/issues/I65N2M" target="_blank">添加作者微信，备注MPJ，加入微信群</a>
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<br/>
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||||
<img width="200px" src="https://mybatisplusjoin.com/qr.png" alt="添加作者微信，备注MPJ，加入微信群"/>
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||||
</p>
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### <a href="https://www.baidu.com/link?url=6NtKqbGKUIIdwoBUaqNkQnLiG3d5y03L6Pfg6ODId0VKfPifpB1xqdQzsBprm-0h&wd=&eqid=d26e7f1600004777000000056440ade6" target="_blank">使用文档WIKI</a>
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