数据库表结构
department
employee
要求一
现在的要求是输入 id 把 employee 表的对应员工数据查询出来，并且查询出该员工的所处部门信息
JavaBean
public class Employee {
private Integer id;
private String lastName;
private String email;
private String gender;
private Department dept;
setter和getter.......
}
public class Department {
private Integer id;
private String departmentName;
setter和getter.......
}
1、级联属性封装结果集
实现
这个要求很明显就要用到两个表，想要把部门信息封装到
Employee对象的dept字段需要用到resultMap属性
方法一
select e.*, d.id did, d.department_name
from employee e,
department d
where e.d_id = d.id
and e.id = #{id}
方法二
select e.*, d.id did, d.department_name
from employee e,
department d
where e.d_id = d.id
and e.id = #{id}
测试
@Test
public void test1() {
SqlSession sqlSession = MyTest.getSqlSession();
EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
System.out.println(mapper.getEmployee(1));
}
结果
2、分步查询
方法
DepartmentMapper.xml
select * from department where id = #{id}
EmployeeMaper.xml
select * from employee where id = #{id}
测试
@Test
public void test1() {
SqlSession sqlSession = MyTest.getSqlSession();
EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
System.out.println(mapper.getEmployee2(1));
}
结果
要求二
现在的要求是输入 id 把 department 表对应的部门信息查询出来，并且查询该部门下的所有员工信息
JavaBean
public class Employee {
private Integer id;
private String lastName;
private String email;
private String gender;
setter和getter.......
}
public class Department {
private Integer id;
private String departmentName;
private List employees;
setter和getter.......
}
1、级联属性封装结果集
方法
select d.*, e.id eid, e.last_name, e.email, e.gender
from department d
left join employee e on d.id = e.d_id
where d.id = #{id}
测试
@Test
public void test2() {
SqlSession sqlSession = MyTest.getSqlSession();
DepartmentMapper mapper = sqlSession.getMapper(DepartmentMapper.class);
System.out.println(mapper.getDepartment(1));
}
结果
2、分步查询
EmployeeMaper.xml
select *
from employee
where d_id = #{did}
DepartmentMapper.xml
select *
from department
where id = #{id}
测试
@Test
public void test2() {
SqlSession sqlSession = MyTest.getSqlSession();
DepartmentMapper mapper = sqlSession.getMapper(DepartmentMapper.class);
System.out.println(mapper.getDepartment3(1));
}
结果
Original: https://www.cnblogs.com/workhah/p/15759172.html
Author: WorkHaH
Title: Mybatis的联合查询
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