你还在手写 join 联表查询？MyBatis-Plus 这样写太香了！
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
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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.provinceFROM user t LEFT JOIN user_address addr on t.id = addr.user_id RIGHT JOIN area a on addr.area_id = a.idWHERE ( addr.tel LIKE ? AND a.province
页:
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