MyBatis之多表关联查询

1使用resultType、ResultMap处理返回结果

处理返回结果

resultType:指定返回值结果的完全限定名,处理多表查询的结果。

多表查询需要定义vo封装查询的结果。

需求：查询部门和部门下对应的岗位

部门名称     岗位名称

办公室        职员

办公室        主人

1.1 建立Post的实体类

 package org.guangsoft.entity;
 /**
  * 岗位的实体类
  * @author guanghe
  */
 public class Post
 {
     private Integer pid;
     private String pname;
     private String pdesc;
     public Integer getPid()
     {
         return pid;
     }
     public void setPid(Integer pid)
     {
         this.pid = pid;
     }
     public String getPname()
     {
         return pname;
     }
     public void setPname(String pname)
     {
         this.pname = pname;
     }
     public String getPdesc()
     {
         return pdesc;
     }
     public void setPdesc(String pdesc)
     {
         this.pdesc = pdesc;
     }

 }

1.2DeptMapper接口添加方法

 package org.guangsoft.mapper;

 import java.util.List;

 import org.guangsoft.entity.Dept;
 import org.guangsoft.vo.DeptVo;

 public interface DeptMapper
 {
     public List<DeptVo> getDeptPost();

     public List<Dept> getDeptPostList();
 } 

1.3DeptMapperImpl中重写方法

 package org.guangsoft.mapper.impl;

 import java.util.List;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 import org.guangsoft.entity.Dept;
 import org.guangsoft.mapper.DeptMapper;
 import org.guangsoft.vo.DeptVo;

 public class DeptMapperImpl implements DeptMapper
 {

     @Override
     public List<DeptVo> getDeptPost()
     {
         //创建sqlSessionFactory对象
         SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder();
         SqlSessionFactory ssf = ssfb.build(DeptMapperImpl.class.
                 getClassLoader().getResourceAsStream("MyBatis.xml"));
         //产生SqlSesion兑现
         SqlSession sqlSession = ssf.openSession();
         //进行数据的crud操作
         List<DeptVo> dlist = sqlSession.selectList("dept.getDeptPost");
         //提交事务
         sqlSession.commit();
         //释放资源
         sqlSession.close();
         return dlist;
     }

     @Override
     public List<Dept> getDeptPostList()
     {
         SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder();
         SqlSessionFactory ssf = ssfb.build(DeptMapperImpl.class.
                 getClassLoader().getResourceAsStream("MyBatis.xml"));
         //产生SqlSesion兑现
         SqlSession sqlSession = ssf.openSession();
         //进行数据的crud操作
         List<Dept> dlist = sqlSession.selectList("dept.getDeptPostList");
         //提交事务
         sqlSession.commit();
         //释放资源
         sqlSession.close();
         return dlist;
     }

 }

1.4建立Post岗位信息表

 /*
 Navicat MySQL Data Transfer

 Source Server         : MySQL
 Source Server Version : 50715
 Source Host           : localhost:3306
 Source Database       : test

 Target Server Type    : MYSQL
 Target Server Version : 50715
 File Encoding         : 65001

 Date: 2016-12-13 20:50:00
 */

 SET FOREIGN_KEY_CHECKS=0;

 -- ----------------------------
 -- Table structure for post
 -- ----------------------------
 DROP TABLE IF EXISTS `post`;
 CREATE TABLE `post` (
   `pid` int(11) NOT NULL AUTO_INCREMENT,
   `pname` varchar(255) DEFAULT NULL,
   `pdesc` varchar(255) DEFAULT NULL,
   `did` int(11) DEFAULT NULL,
   PRIMARY KEY (`pid`),
   KEY `fk_did` (`did`),
   CONSTRAINT `fk_did` FOREIGN KEY (`did`) REFERENCES `dept` (`did`)
 ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

1.5DeptMapper.xml定义操作

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 <mapper namespace="dept">
     <select id="getDeptPost" resultType="org.guangsoft.vo.DeptVo">
         select did,dname,pname from dept inner join post on dept.did = post.did
     </select>
     <resultMap type="org.guangsoft.entity.Dept" id="deptPost">
         <id property="did" column="did"></id>
         <result property="dname" column="dname" javaType="java.lang.String"></result>
         <collection property="posts" ofType="org.guangsoft.entity.Post">
             <id property="pid" column="pid"></id>
             <result property="pname" column="pname" javaType="java.lang.String"></result>
             <result property="pdesc" column="pdesc" javaType="java.lang.String"></result>
         </collection>
     </resultMap>
     <select id="getDeptPostList" resultMap="deptPost">
         select * from dept inner join post
         on dept.did = post.did
     </select>
 </mapper>

1.6添加测试方法

 package org.guangsoft.test;

 import java.util.List;

 import org.guangsoft.entity.Dept;
 import org.guangsoft.entity.Post;
 import org.guangsoft.mapper.DeptMapper;
 import org.guangsoft.mapper.impl.DeptMapperImpl;
 import org.guangsoft.vo.DeptVo;
 import org.junit.Test;

 public class TestDeptMapper
 {
     DeptMapper deptMapper = new DeptMapperImpl();

     @Test
     public void testGetDeptVo()
     {
         List<DeptVo> dlist = deptMapper.getDeptPost();
         for(DeptVo deptVo : dlist)
         {
             System.out.println(deptVo.getDid() +
                 " " + deptVo.getDname() + deptVo.getPname());
         }
     }

     @Test
     public void testGetDeptList()
     {
         List<Dept> dlist = deptMapper.getDeptPostList();
         for(Dept dept : dlist)
         {
             System.out.println(dept.getDname());
             List<Post> postList = dept.getPosts();
             for(Post post : postList)
             {
                 System.out.println(post.getPname());
             }
         }
     }

 } 

2返回值结果的处理总结

使用resultType:指定的是返回值类型的完全限定名，只能用在单表查询或者定义vo的情况，如果是定义vo不能将关联的数据封装为需要获得某个类的对象

使用resultMap：不需要定义vo类，将关联数据对应的类，作为另外一个类的属性。

第一步：定义resultMap

第二步：引用resultMap

使用resultMap：用来多表关联的复杂查询中，通过需要将关联查询的数据封装为某个实体类对象，如果有特殊业务需要或者说明需要将管理数据封装为实体类的对象，使用resultMap