mybatis-plus-join

gitee
github

使用方法

安装

在项目中添加依赖

    com.github.yulichang

    mybatis-plus-join

    1.2.2

/pre>
p>或者clone代码到本地,执行mvn install,再引入以上依赖
/p>
p> 注意: mybatis plus version >= 3.4.0
/p>
h4>使用
/h4>
p>mapper继承MPJBaseMapper (必选)
/p>
p>service继承MPJBaseService (可选)
/p>
p>serviceImpl继承MPJBaseServiceImpl (可选)
/p>
h3>核心类 MPJLambdaWrapper和MPJQueryWrapper
/h3>
h4>MPJLambdaWrapper用法
/h4>
h5>MPJLambdaWrapper示例
/h5>
h5>简单的3表查询
/h5>
pre class='language-javascript'>
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

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

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

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

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