現在有員工和部門兩張表，前兩篇文章介紹的都是根據員工查部門，本篇文章介紹由部門查所有員工

首先請參照上上篇中步驟1，2，3 , 4，此處從第5步開始

一、巢狀查詢

5.新增DepartmentMapper.java介面方法

public interface DepartmentMapper {	
	public Department getDeptByIdPlus(Integer id);
}

6.新增DepartmentMapper.xml檔案，配置資訊如下

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.atguigu.mybatis.dao.DepartmentMapper">

	<!-- collection巢狀結果集的方式，定義關聯的集合型別元素的封裝規則-->
	
	<!-- 巢狀結果集的方式，使用collection標籤定義關聯的集合型別的屬性封裝規則 -->
	<resultMap type="com.atguigu.mybatis.bean.Department" id="MyDept">
		<id column="did" property="id"/>
		<result column="dept_name" property="departmentName"/>
		<!-- 
		collection定義關聯結合型別的屬性的封裝規則
		ofType：指定集合裡面元素的型別
		-->
		<collection property="emps" ofType="com.atguigu.mybatis.bean.Employee">
			<!-- 定義這個集合中元素的封裝規則 -->
			<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,
			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>
	
</mapper>
 

7.新增測試方法

	@Test
	public void test06() throws IOException{
		
		SqlSessionFactory sqlSesssionFactory = getSqlSesssionFactory();
		SqlSession openSession = sqlSesssionFactory.openSession();
		try {
			DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);
			Department deptByIdPlus = mapper.getDeptByIdPlus(2);
			System.out.println(deptByIdPlus);
			System.out.println(deptByIdPlus.getEmps());
			
		} finally {
			openSession.close();
		}
	}
 

8.控制檯資訊

二、分段查詢

5.新增EmployeeMapperPlus.xml檔案，配置資訊如下

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperPlus">
	<select id="getEmpsByDeptId" resultType="com.atguigu.mybatis.bean.Employee">
	 	select * from tbl_employee where d_id=#{deptId}
	 </select>
<mapper/>

6.DepartmentMapper.xml檔案，配置資訊

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.atguigu.mybatis.dao.EmployeeMapperPlus">
	
<resultMap type="com.atguigu.mybatis.bean.Department" id="MyDeptStep">
		<id column="id" property="id"/>
		<id column="dept_name" property="departmentName"/>
		<collection property="emps"
			select="com.atguigu.mybatis.dao.EmployeeMapperPlus.getEmpsByDeptId"
			column="{deptId=id}" fetchType="lazy"></collection>
</resultMap>
	<!-- public Department getDeptByIdStep(Integer id); -->
	<select id="getDeptByIdStep" resultMap="MyDeptStep">
		select id,dept_name departmentName from tbl_dept where id=#{id}
	</select>

<mapper/>

7.新增測試方法

@Test
	public void test06() throws IOException{
		
		SqlSessionFactory sqlSesssionFactory = getSqlSesssionFactory();
		SqlSession openSession = sqlSesssionFactory.openSession();
		try {
			DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);
			Department deptByIdStep = mapper.getDeptByIdStep(1);
			System.out.println(deptByIdStep);		
		} finally {
			openSession.close();
		}
	}

8.控制檯資訊：分步查詢效果