# 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)
```