Mybatis联合查询的实现方法

目录

• 1、级联属性封装结果集
• 实现
• 2、分步查询
• 方法
• 3、级联属性封装结果集
• 4、分步查询

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

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

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.......
}

3、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

4、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

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