Mybatis-Plus查询返回Map类型数据

Mybatis-Plus查询返回Map类型数据

我们前面的案例都是返回的集合List；

集合List的弊端是会把所有的列属性都封装返回，但是我们有时候，只需要返回几个字段，然后再返回到用户端；

所以mp框架给我们提供了List>返回类型，String是列名，Object是值，只返回select的字段；

举例：

@Test
public void selectByQueryWrapper9(){
    QueryWrapper queryWrapper=new QueryWrapper();
    // QueryWrapper queryWrapper2=Wrappers.query();
    queryWrapper
             .select("department_id","AVG(salary) AS avg_salary")
             .groupBy("department_id");
    List employeeList = employeeMapper.selectList(queryWrapper);
    System.out.println(employeeList);
}

返回值：

[Employee(id=null, name=null, birthday=null, gender=null, email=null, phoneNumber=null, salary=null, department_id=1, avg_salary=3000.0000), Employee(id=null, name=null, birthday=null, gender=null, email=null, phoneNumber=null, salary=null, department_id=2, avg_salary=3765.0000), Employee(id=null, name=null, birthday=null, gender=null, email=null, phoneNumber=null, salary=null, department_id=3, avg_salary=4000.0000), Employee(id=null, name=null, birthday=null, gender=null, email=null, phoneNumber=null, salary=null, department_id=4, avg_salary=5000.0000)]

没用的字段也返回了；

我们改用Map`

@Test
public void selectByQueryWrapper10ReturnMap(){
    QueryWrapper queryWrapper=new QueryWrapper();
    // QueryWrapper queryWrapper2=Wrappers.query();
    queryWrapper
             .select("department_id","AVG(salary) AS avg_salary")
             .groupBy("department_id");
    List> maps = employeeMapper.selectMaps(queryWrapper);
    System.out.println(maps);
}

返回结果：

[{department_id=1, avg_salary=3000.0000}, {department_id=2, avg_salary=3765.0000}, {department_id=3, avg_salary=4000.0000}, {department_id=4, avg_salary=5000.0000}]

这样的结果才比较友好；