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);
}

EmpDao.java

<!-- 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>

@Testpublic 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>

DeptMapper.xml

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>

DeptMapper.xml

/*** 一对多嵌套结果映射* 查询部门及部门下所有的员工* */@Testpublic 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());    }}