mybatis-plus-join

支持连表查询的mybatis-plus

运行环境

• mysql8
• jdk8
• mybatis-plus 3.4.2

使用方法

方法一

1. 将代码down到本地，使用maven install

2. 在自己的项目中替换mybatisplus依赖(框架依赖mybatisplus<3.4.2>)

   <dependency>
       <groupId>com.github.mybatisplus</groupId>
       <artifactId>join</artifactId>
       <version>1.0-SNAPSHOT</version>
   </dependency>
   

方法二

1. 将mybatisplus目录复制到你的工程中

2. 如果mybatisplus目录不在springboot扫描路径下,
   将MybatisPlusConfiguration移动到springboot扫描路径下或添加springboot扫描路径

3. 添加cglib依赖

   <dependency>
       <groupId>cglib</groupId>
       <artifactId>cglib</artifactId>
       <version>3.3.0</version>
   </dependency>
   

使用

• mapper继承MyBaseMapper (必选)
• service继承MyBaseService (可选)
• serviceImpl继承MyBaseServiceImpl (可选)

MyLambdaQueryWrapper用法

select(UserEntity::getId) 查询指定的字段,支持可变参数

简单的3表查询

class test {
    @Resource
    private UserMapper userMapper;

    void testJoin() {
        List<UserDTO> list = userMapper.selectJoinList(new MyLambdaQueryWrapper<UserEntity>()
                        .selectAll(UserEntity.class)
                        .leftJoin(UserEntity::getId, UserAddressEntity::getUserId,
                                r1 -> r1.select(UserAddressEntity::getAddress)
                                        .leftJoin(UserAddressEntity::getAreaId, AreaEntity::getId,
                                                r2 -> r2.select(AreaEntity::getProvince)))
                , UserDTO.class);
    }
}

对应sql

SELECT t0.name,
       t0.sex,
       t0.head_img,
       t0.id,
       t1.address,
       t2.province
FROM user t0
         LEFT JOIN user_address t1 ON t0.id = t1.user_id
         LEFT JOIN area t2 ON t1.area_id = t2.id

sql -> 伪代码

class test {
    void testJoin() {
        List<UserDTO> list = userMapper.selectJoinList(new MyLambdaQueryWrapper<user表>()
                        .selectAll(user表实体类.class)//查询user表全部字段
                        .leftJoin(user表on字段, user_address表on字段,
                                user_address表对象 -> user_address表对象
                                        .select(user_address表address字段)
                                        .leftJoin(user_address表表的on字段, area表的on字段,
                                                area表对象 -> area表对象.select(area表的province字段)))
                , UserDTO.class);//返回对象class
    }
}

selectAll() 查询UserEntity全部字段

查询user全部字段和user_address表中的address,tel

class test {
    @Resource
    private UserMapper userMapper;

    void testJoin() {
        List<UserDTO> list = userMapper.selectJoinList(new MyLambdaQueryWrapper<UserEntity>()
                        .selectAll(UserEntity.class)
                        .leftJoin(UserEntity::getId, UserAddressEntity::getUserId,
                                right -> right.select(UserAddressEntity::getAddress, UserAddressEntity::getTel))
                , UserDTO.class);
    }
}

对应sql

SELECT t0.name,
       t0.sex,
       t0.head_img,
       t0.id,
       t1.address,
       t1.tel
FROM user t0
         LEFT JOIN user_address t1 ON t0.id = t1.user_id

as(UserEntity::getHeadImg,UserDTO::getUserHeadImg)

查询字段别名 head_img as userHeadImg

class test {
    @Resource
    private UserMapper userMapper;

    void testJoin() {
        List<UserDTO> list = userMapper.selectJoinList(new MyLambdaQueryWrapper<UserEntity>()
                        .as(UserEntity::getHeadImg, UserDTO::getUserHeadImg)
                        .leftJoin(UserEntity::getId, UserAddressEntity::getUserId,
                                right -> right.select(UserAddressEntity::getAddress, UserAddressEntity::getTel))
                , UserDTO.class);
    }
}

对应sql

SELECT t0.head_img AS userHeadImg,
       t1.address,
       t1.tel
FROM user t0
         LEFT JOIN user_address t1 ON t0.id = t1.user_id

左连接 leftJoin(UserEntity::getId,UserAddressEntity::getUserId,right -> right)

前连个参数是两个表的连接条件:
user left join user_address on user.id = User_address.user_id
第三个参数是右表wrapper对象,可以继续使用,以上方法.

条件查询eq()

class test {
    @Resource
    private UserMapper userMapper;

    void testJoin() {
        List<UserDTO> list = userMapper.selectJoinList(new MyLambdaQueryWrapper<UserEntity>()
                        .selectAll(UserEntity.class)
                        .leftJoin(UserEntity::getId, UserAddressEntity::getUserId,
                                right -> right.select(UserAddressEntity::getAddress, UserAddressEntity::getTel))
                        .eq(true, UserEntity::getId, 1)
                        .like(UserAddressEntity::getTel, "1")
                        .eq(UserEntity::getId, UserAddressEntity::getUserId)
                , UserDTO.class);
    }
}

对应sql

SELECT t0.name,
       t0.sex,
       t0.head_img,
       t0.id,
       t1.address,
       t1.tel
FROM user t0
         LEFT JOIN user_address t1 ON t0.id = t1.user_id
WHERE (
              t0.id = ?
              AND t1.tel LIKE ?
              AND t0.id = t1.user_id)

参考测试类