# mybatis-plus-join 支持连表查询的[mybatis-plus](https://gitee.com/baomidou/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. 在自己的项目中添加依赖 ```xml com.github.mybatisplus join 1.0-SNAPSHOT ``` ### 方法二 1. 将mybatisplus目录复制到你的工程中的springboot扫描路径下 2. 添加cglib依赖 ```xml cglib cglib 3.3.0 ``` ### 使用 * mapper继承MyBaseMapper (必选) * service继承MyBaseService (可选) * serviceImpl继承MyBaseServiceImpl (可选) ## MyQueryWrapper用法 简单的3表查询 ```java class test { @Resource private UserMapper userMapper; void testJoin() { List list = userMapper.selectJoinList(UserDTO.class, new MyLambdaQuery() .selectAll(UserDO.class) .select("addr.tel", "addr.address") .select("a.province") .leftJoin("user_address addr on t.id = addr.user_id") .rightJoin("area a on addr.area_id = a.id") .eq(true, UserDO::getId, 1) .stringQuery() .like(true, "addr.tel", "1") .le(true, "a.province", "1")); } } ``` 对应sql ```sql SELECT t.id, t.name, t.sex, t.head_img, addr.tel, addr.address, a.province FROM user t LEFT JOIN user_address addr on t.id = addr.user_id RIGHT JOIN area a on addr.area_id = a.id WHERE ( t.id = ? AND addr.tel LIKE ? AND a.province <= ?) ``` 说明: * UserDTO.class 查询结果类(resultType) * selectAll(UserDO.class) 查询主表全部字段(主表实体类) * select() mp的select策略是覆盖,这里的策略是追加,可以一直select 主表字段可以用lambda,会自动添加表别名,主表别名默认是 t ,非主表字段必须带别名查询 * leftJoin() rightJoin() innerJoin() 传sql片段 格式 (表 + 别名 + 关联条件) * stringQuery() lambda查询转string查询 * lambda() string查询转lambda查询 * sql组装由mp完成,正常使用没有sql注入风险 分页查询 ```java class test { @Resource private UserMapper userMapper; void testJoin() { IPage page = userMapper.selectJoinPage(new Page<>(1, 10), UserDTO.class, new MyLambdaQuery() .selectAll(UserDO.class) .select("addr.tel", "addr.address") .select("a.province") .leftJoin("user_address addr on t.id = addr.user_id") .rightJoin("area a on addr.area_id = a.id")); } } ``` 对应sql ```sql SELECT t.id, t.name, t.sex, t.head_img, addr.tel, addr.address, a.province FROM user t LEFT JOIN user_address addr on t.id = addr.user_id RIGHT JOIN area a on addr.area_id = a.id LIMIT ?,? ``` 还可以怎么操作,但不建议 ```java class test { @Resource private UserMapper userMapper; void testJoin() { List list = userMapper.selectJoinList(UserDTO.class, new MyLambdaQuery() .selectAll(UserDO.class) .select("addr.tel", "addr.address") //行列转换 .select("CASE t.sex WHEN '男' THEN '1' ELSE '0' END AS sex") //求和函数 .select("sum(a.province) as province") //自定义数据集 .leftJoin("(select * from user_address) addr on t.id = addr.user_id") .rightJoin("area a on addr.area_id = a.id") .eq(true, UserDO::getId, 1) .stringQuery() .like(true, "addr.tel", "1") .le(true, "a.province", "1") .orderByDesc("addr.id")); } } ``` 对应sql ```sql SELECT t.id, t.name, t.sex, t.head_img, addr.tel, addr.address, CASE t.sex WHEN '男' THEN '1' ELSE '0' END AS sex, sum(a.province) as province FROM user t LEFT JOIN (select * from user_address) addr on t.id = addr.user_id RIGHT JOIN area a on addr.area_id = a.id WHERE ( t.id = ? AND addr.tel LIKE ? AND a.province <= ?) ORDER BY addr.id DESC ``` # MyLambdaQueryWrapper用法 ### MyLambdaQueryWrapper更符合面向对象(OOP),没有难以理解的常量(魔术值),全部基于lambda,但好像不那么好理解 简单的3表查询 ```java class test { @Resource private UserMapper userMapper; void testJoin() { List list = userMapper.selectJoinList(new MyLambdaQueryWrapper() .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 ```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 ```java class test { void testJoin() { List list = userMapper.selectJoinList(new MyLambdaQueryWrapper() .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 } } ``` 查询user全部字段和user_address表中的address,tel ```java class test { @Resource private UserMapper userMapper; void testJoin() { List list = userMapper.selectJoinList(UserDTO.class, new MyLambdaQueryWrapper() .selectAll(UserEntity.class) .leftJoin(UserEntity::getId, UserAddressEntity::getUserId, right -> right.select(UserAddressEntity::getAddress, UserAddressEntity::getTel))); } } ``` 对应sql ```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 ``` 查询字段别名 head_img as userHeadImg ```java class test { @Resource private UserMapper userMapper; void testJoin() { List list = userMapper.selectJoinList(UserDTO.class, new MyLambdaQueryWrapper() .as(UserEntity::getHeadImg, UserDTO::getUserHeadImg) .leftJoin(UserEntity::getId, UserAddressEntity::getUserId, right -> right.select(UserAddressEntity::getAddress, UserAddressEntity::getTel))); } } ``` 对应sql ```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. 连表条件查询 ```java class test { @Resource private UserMapper userMapper; void testJoin() { List list = userMapper.selectJoinList(UserDTO.class, new MyLambdaQueryWrapper() .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)); } } ``` 对应sql ```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) ```