MyBatis_collection定义关联集合封装规则

一个部门下有很多员工,这么多员工就可以封装为一个集合来处理
现在我们要在查部门时把当前部门的所有员工查出来
在Department.java中添加属性还有对应的get,set方法:

    private List<Employee> emps;
    public List<Employee> getEmps() {
        return emps;
    }
    public void setEmps(List<Employee> emps) {
        this.emps = emps;
    }

在接口DepartmentMapper.java中写方法:

public Department getDeptByIdPlus(Integer id);

然后在DepartmentMapper.xml中实现方法:

<!--嵌套结果集的方式，使用collection标签定义关联的集合类型的属性封装规则  -->
    <resultMap type="com.atguigu.mybatis.bean.Department" id="MyDept">
        <id column="did" property="id"/>
        <result column="dept_name" property="departmentName"/>
        <!-- 
            collection定义关联集合类型的属性的封装规则 
            ofType:指定集合里面元素的类型
        -->
        <collection property="emps" ofType="com.atguigu.mybatis.bean.Employee">
            <!-- 定义这个集合中元素的封装规则 -->
            <id column="eid" property="id"/>
            <result column="last_name" property="lastName"/>
            <result column="email" property="email"/>
            <result column="gender" property="gender"/>
        </collection>
    </resultMap>
    <!-- public Department getDeptByIdPlus(Integer id); -->
    <select id="getDeptByIdPlus" resultMap="MyDept">
        SELECT d.id did,d.dept_name dept_name,
               e.id eid,e.last_name last_name,e.email email,e.gender gender
        FROM tbl_dept d
        LEFT JOIN tbl_employee e
        ON d.id=e.d_id
        WHERE d.id=#{id}
    </select>

测试一下:

    @Test
    public void test06() throws IOException{
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession();
        try{
            DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);
            Department department = mapper.getDeptByIdPlus(1);
            System.out.println(department);
            System.out.println(department.getEmps());
        }finally{
            openSession.close();
        }
    }