使用方法

安装

Maven

<dependency>
    <groupId>com.github.yulichang</groupId>
    <artifactId>mybatis-plus-join</artifactId>
    <version>1.2.4</version>
</dependency>

Gradle

 implementation 'com.github.yulichang:mybatis-plus-join:1.2.4'

或者clone代码到本地执行 mvn install, 再引入以上依赖

注意: mybatis plus version >= 3.4.0

推荐一个开源免费的 Spring Boot 最全教程：

https://github.com/javastacks/spring-boot-best-practice

使用

• mapper继承MPJBaseMapper (必选)
• service继承MPJBaseService (可选)
• serviceImpl继承MPJBaseServiceImpl (可选)

核心类 MPJLambdaWrapper和MPJQueryWrapper

MPJLambdaWrapper用法

简单的三表查询

class test {
    @Resource
    private UserMapper userMapper;

    void testJoin() {
        List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
                new MPJLambdaWrapper<UserDO>()
                        .selectAll(UserDO.class)
                        .select(UserAddressDO::getTel)
                        .selectAs(UserAddressDO::getAddress, UserDTO::getUserAddress)
                        .select(AreaDO::getProvince, AreaDO::getCity)
                        .leftJoin(UserAddressDO.class, UserAddressDO::getUserId, UserDO::getId)
                        .leftJoin(AreaDO.class, AreaDO::getId, UserAddressDO::getAreaId)
                        .eq(UserDO::getId, 1)
                        .like(UserAddressDO::getTel, "1")
                        .gt(UserDO::getId, 5));
    }
}

对应sql

SELECT 
    t.id,
    t.name,
    t.sex,
    t.head_img,
    t1.tel,
    t1.address AS userAddress,
    t2.province,
    t2.city 
FROM 
    user t 
    LEFT JOIN user_address t1 ON t1.user_id = t.id 
    LEFT JOIN area t2 ON t2.id = t1.area_id 
WHERE (
    t.id = ? 
    AND t1.tel LIKE ? 
    AND t.id > ?)

说明:

• UserDTO.class 查询结果返回类(resultType)
• selectAll() 查询指定实体类的全部字段
• 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
  故将UserAddressDO和AreaDO分开为两个select()
• 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
• leftJoin() 参数说明
  第一个参数: 参与连表的实体类class
  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
  第三个参数: 参与连表的ON的另一个实体类属性
• 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....
• 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

分页查询

class test {
    @Resource
    private UserMapper userMapper;

    void testJoin() {
        IPage<UserDTO> iPage = userMapper.selectJoinPage(new Page<>(2, 10), UserDTO.class,
                new MPJLambdaWrapper<UserDO>()
                        .selectAll(UserDO.class)
                        .select(UserAddressDO::getTel)
                        .selectAs(UserAddressDO::getAddress, UserDTO::getUserAddress)
                        .select(AreaDO::getProvince, AreaDO::getCity)
                        .leftJoin(UserAddressDO.class, UserAddressDO::getUserId, UserDO::getId)
                        .leftJoin(AreaDO.class, AreaDO::getId, UserAddressDO::getAreaId));
    }
}

对应sql

SELECT 
    t.id,
    t.name,
    t.sex,
    t.head_img,
    t1.tel,
    t1.address AS userAddress,
    t2.province,
    t2.city
FROM 
    user t
    LEFT JOIN user_address t1 ON t1.user_id = t.id
    LEFT JOIN area t2 ON t2.id = t1.area_id
LIMIT ?,?

MPJQueryWrapper

简单的3表查询

class test {
    @Resource
    private UserMapper userMapper;

    void testJoin() {
        List<UserDTO> list = userMapper.selectJoinList(UserDTO.class,
                new MPJQueryWrapper<UserDO>()
                        .selectAll(UserDO.class)
                        .select("addr.tel", "addr.address", "a.province")
                        .leftJoin("user_address addr on t.id = addr.user_id")
                        .rightJoin("area a on addr.area_id = a.id")
                        .like("addr.tel", "1")
                        .le("a.province", "1"));
    }
}

对应sql

SELECT 
    t.id,
    t.name,
    t.sex,
    t.head_img,
    addr.tel,
    addr.address,
    a.province
FROM 
    user t
    LEFT JOI