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