嵌套映射

1. 多对一嵌套查询映射使用案例

package com.zixue.dao;


import com.zixue.annotation.MyBatisRepository;
import com.zixue.entity.Emp;

/**
 * 员工表的DAO组件
 * */
@MyBatisRepository
public interface EmpDao {

    void save(Emp emp);
    
    Emp findById(int id);
    Emp findById2(int id);
}

<!-- 使用嵌套查询 在查询一条员工数据时 关联查询出对应的部门 -->
 <select id="findById" parameterType="java.lang.Integer" 
  resultMap="empMap">
  select * from t_emp where empno=#{id}
  </select>
  <select id="findDept" parameterType="java.lang.Integer" 
   resultType="com.zixue.entity.Dept">
   select * from t_dept where deptno=#{deptno}
   </select>
   <resultMap type="com.zixue.entity.Emp" id="empMap">
       <association property="dept" column="deptno" 
       javaType="com.zixue.entity.Dept" select="findDept">
       </association>
   </resultMap>

2.多对一嵌套结果映射使用案例

 <!-- 使用嵌套结果 在查询一条员工数据时 关联查询出对应的部门 -->
   <select id="findById2" parameterType="java.lang.Integer" 
    resultMap="empMap">
    select e.*,d.*  from t_emp e inner join t_dept d on e.deptno=d.deptno where e.empno=#{id}
    </select>
    <resultMap type="com.zixue.entity.Emp" id="empMap2">
    <id property="empno" column="empno"/>
    <result property="ename" column="ename"/>
    <result property="job" column="job"/>
    <result property="mgr" column="mgr"/>
    <result property="hiredate" column="hiredate"/>
    <result property="sal" column="sal"/>
    <result property="comm" column="comm"/>
    <result property="deptno" column="deptno"/>
    
    <association property="dept" column="deptno" javaType="com.zixue.entity.Dept">
    <id property="deptno" column="deptno"/>
    <result property="dname" column="dname"/>
    <result property="loc" column="loc"/>
    </association>
    </resultMap>

@Test
    public void testFindById2(){
        ApplicationContext ac =new ClassPathXmlApplicationContext("applicationContext.xml");
        EmpDao dao =ac.getBean(EmpDao.class);
        Emp e =dao.findById(100);
        System.out.println(
        e.getEname()+" "+e.getJob()+" "+e.getEmpno()+" "+e.getDept().getDeptno()+" "+e.getDept().getDname()        
        );

 3.一对多嵌套查询映射

/**
	 * 关联属性 用于封装部门对应的员工信息
	 * */
	private List<Emp> emps;

　　

package com.zixue.dao;

import com.zixue.annotation.MyBatisRepository;
import com.zixue.entity.Dept;

@MyBatisRepository
public interface DeptDao {
	
	Dept findById(int id);
	
	Dept findById2(int id);
}

　　

<mapper namespace="com.zixue.dao.DeptDao">
<!-- 嵌套查询 -->
<select id="findById" parameterType="java.lang.Integer" resultMap="deptMap">
select * from t_dept where deptno=#{id}
</select>
<select id="findEmps" parameterType="java.lang.Integer" resultType="com.zixue.entity.Emp">
select * from t_emp where deptno=#{deptno}
</select>
<resultMap type="com.zixue.entity.Dept" id="deptMap">
<id property="deptno" column="deptno"/>
<collection property="emps" column="deptno" javaType="java.util.ArrayList" 
 select="findEmps" ofType="com.zixue.entity.Emp">
 </collection>
</resultMap>

4.一对多嵌套结果查询

<!-- 嵌套结果 -->
<select id="findById2" parameterType="java.lang.Integer" 
 resultMap="deptMap2">
 select d.*,e.* from t_dept d inner join t_emp e on d.deptno=e.deptno where d.deptno=#{id}
 </select>
 <resultMap type="com.zixue.entity.Dept" id="deptMap2">
 <id property="deptno" column="deptno"/>
 <result property="dname" column="dname" jdbcType="VARCHAR" javaType="string"/>
 <result property="loc" column="loc" jdbcType="VARCHAR" javaType="string"/>
 <collection property="emps" ofType="com.zixue.entity.Emp" 
  javaType="java.util.ArrayList" column="deptno">
  <id property="empno" column="empno"/>
  <result property="ename" column="ename"/>
  <result property="job" column="job"/>
  <result property="mgr" column="mgr"/>
  <result property="hiredate" column="hiredate"/>
  <result property="sal" column="sal"/>
  <result property="comm" column="comm"/>
  <result property="deptno" column="deptno"/>
  </collection>
 </resultMap>

/**
     * 一对多嵌套结果映射
     * 查询部门及部门下所有的员工
     * */
    @Test
    public void testFindEmps2(){
        ApplicationContext ac =new ClassPathXmlApplicationContext("applicationContext.xml");
        DeptDao dao =ac.getBean(DeptDao.class);
        Dept d =dao.findById2(10);
        System.out.println(
        d.getDeptno()+" "+d.getDname()+" "+d.getLoc()        
        );
        List<Emp> emps =d.getEmps();
        for(Emp e: emps){
            System.out.println(e.getEname()+" "+e.getJob()+" "+e.getEmpno());    
        }
    }