Mybatis联合查询怎么实现

本篇内容主要讲解“Mybatis联合查询怎么实现”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“Mybatis联合查询怎么实现”吧!

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

 <!-- public Employee getEmployee(int id); --><select id="getEmployee" resultMap="emp1">select e.*, d.id did, d.department_namefrom employee e,department dwhere e.d_id = d.idand e.id = #{id}</select><resultMap id="emp1" type="employee"><id column="id" property="id"/><result column="last_name" property="lastName"/><result column="email" property="email"/><result column="gender" property="gender"/><result column="did" property="dept.id"/><result column="department_name" property="dept.departmentName"/></resultMap>

方法二

<!-- public Employee getEmployee(int id); --><select id="getEmployee" resultMap="emp2">select e.*, d.id did, d.department_namefrom employee e,department dwhere e.d_id = d.idand e.id = #{id}</select><resultMap id="emp2" type="employee"><id column="id" property="id"/><result column="last_name" property="lastName"/><result column="email" property="email"/><result column="gender" property="gender"/><association property="dept" javaType="department"><id column="did" property="id"/><result column="department_name" property="departmentName"/></association></resultMap>

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

<!-- public Department getDepartment2(int id); --><select id="getDepartment2" resultType="department">select * from department where id = #{id}</select>

EmployeeMaper.xml

<!-- public Employee getEmployee2(int id); --><!-- 分步查询 --><select id="getEmployee2" resultMap="emp3">select * from employee where id = #{id}</select><resultMap id="emp3" type="employee"><id column="id" property="id"/><result column="last_name" property="lastName"/><result column="email" property="email"/><result column="gender" property="gender"/><association property="dept" select=&quot.workhah.mapper.department.DepartmentMapper.getDepartment2" column="d_id"/></resultMap>

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<Employee> employees;    setter和getter.......}

3、级联属性封装结果集

方法

<!--   public Department getDepartment(int id); --><select id="getDepartment" resultMap="dep1">select d.*, e.id eid, e.last_name, e.email, e.genderfrom department dleft join employee e on d.id = e.d_idwhere d.id = #{id}</select><resultMap id="dep1" type="department"><id column="id" property="id"/><result column="department_name" property="departmentName"/><collection property="employees" ofType="employee"><id column="eid" property="id"/><result column="last_name" property="lastName"/><result column="email" property="email"/><result column="gender" property="gender"/></collection></resultMap>

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

<!--  public List<Employee> getEmployeeByDid(int did); --><select id="getEmployeeByDid" resultType="employee">select *from employeewhere d_id = #{did}</select>

DepartmentMapper.xml

<!-- public Department getDepartment3(int id); --><select id="getDepartment3" resultMap="dep2">select *from departmentwhere id = #{id}</select><resultMap id="dep2" type="department"><id column="id" property="id"/><result column="depart_name" property="departName"/><collection property="employees" ofType="employee"select=&quot.workhah.mapper.employee.EmployeeMapper.getEmployeeByDid" column="id"/></resultMap>

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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