# mybatis-plus-join
* 支持连表查询的[mybatis-plus](https://gitee.com/baomidou/mybatis-plus)
* [演示示例](https://gitee.com/best_handsome/mybatis-plus-join-demo)
* 点个Star支持一下吧 :)
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## 使用方法
### 安装
1. 在项目中添加依赖
- Maven
```xml
com.github.yulichang
mybatis-plus-join
1.1.7
```
- Gradle
```
implementation group: 'com.github.yulichang', name: 'mybatis-plus-join', version: '1.1.6'
```
或者clone代码到本地自行安装,再引入以上依赖
注意: mybatis plus version >= 3.4.0
### 使用
* mapper继承MPJBaseMapper (必选)
* service继承MPJBaseService (可选)
* serviceImpl继承MPJBaseServiceImpl (可选)
1. MPJBaseMapper继承BaseMapper,在原有的方法基础上又添加了以下方法:
* selectJoinOne 连表查询一条记录对象
* selectJoinList 连表查询返回命中记录对象集合
* selectJoinPage 连表分页查询对象集合
* selectJoinMap 连表查询一条记录返回Map
* selectJoinMaps 连表查询返回命中记录Map集合
* selectJoinMapsPage 连表分页查询返回Map集合
2. MPJBaseService 继承了IService,同样添加以上方法
3. MPJBaseServiceImpl 继承了ServiceImpl,同样添加了以上方法
## 核心类 MPJLambdaWrapper和MPJQueryWrapper
### MPJLambdaWrapper用法
#### MPJLambdaWrapper示例
#### 简单的3表查询
```java
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
List list = userMapper.selectJoinList(UserDTO.class,
new MPJLambdaWrapper()
.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
```java
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
IPage iPage = userMapper.selectJoinPage(new Page<>(2, 10), UserDTO.class,
new MPJLambdaWrapper()
.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
```java
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
List list = userMapper.selectJoinList(UserDTO.class,
new MPJQueryWrapper()
.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 JOIN user_address addr on t.id = addr.user_id
RIGHT JOIN area a on addr.area_id = a.id
WHERE (
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)默认主表别名 "t"
* select() mp的select策略是覆盖,以最后一次为准,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)
* 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
```java
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
IPage page = userMapper.selectJoinPage(new Page<>(1, 10), UserDTO.class,
new MPJQueryWrapper()
.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
```
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 ?,?
```
#### 还可以这么操作,但不建议
```java
class test {
@Resource
private UserMapper userMapper;
void testJoin() {
List list = userMapper.selectJoinList(UserDTO.class,
new MPJQueryWrapper()
.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")
.like("addr.tel", "1")
.le("a.province", "1")
.orderByDesc("addr.id"));
}
}
```
对应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 (
addr.tel LIKE ?
AND a.province <= ?)
ORDER BY
addr.id DESC
```
# [wiki](https://gitee.com/best_handsome/mybatis-plus-join/wikis)