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;  2 /**
 * 岗位的实体类  4  * @author guanghe  5  */
public class Post  7 {  8     private Integer pid;  9     private String pname; 10     private String pdesc; 11     public Integer getPid() 12  { 13         return pid; 14  } 15     public void setPid(Integer pid) 16  { 17         this.pid = pid; 18  } 19     public String getPname() 20  { 21         return pname; 22  } 23     public void setPname(String pname) 24  { 25         this.pname = pname; 26  } 27     public String getPdesc() 28  { 29         return pdesc; 30  } 31     public void setPdesc(String pdesc) 32  { 33         this.pdesc = pdesc; 34  } 35     
}

1.2DeptMapper接口添加方法

package org.guangsoft.mapper;  2 
import java.util.List;  4 
import org.guangsoft.entity.Dept;  6 import org.guangsoft.vo.DeptVo;  7 
public interface DeptMapper  9 { 10     public List<DeptVo> getDeptPost(); 11 
    public List<Dept> getDeptPostList(); 13 } 

1.3DeptMapperImpl中重写方法

package org.guangsoft.mapper.impl;  2 
import java.util.List;  4 
import org.apache.ibatis.session.SqlSession;  6 import org.apache.ibatis.session.SqlSessionFactory;  7 import org.apache.ibatis.session.SqlSessionFactoryBuilder;  8 import org.guangsoft.entity.Dept;  9 import org.guangsoft.mapper.DeptMapper; 10 import org.guangsoft.vo.DeptVo; 11 
public class DeptMapperImpl implements DeptMapper 13 { 14     
 @Override 16     public List<DeptVo> getDeptPost() 17  { 18         //创建sqlSessionFactory对象
        SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder(); 20         SqlSessionFactory ssf = ssfb.build(DeptMapperImpl.class. 21                 getClassLoader().getResourceAsStream("MyBatis.xml")); 22         //产生SqlSesion兑现
        SqlSession sqlSession = ssf.openSession(); 24         //进行数据的crud操作
        List<DeptVo> dlist = sqlSession.selectList("dept.getDeptPost"); 26         //提交事务
 sqlSession.commit(); 28         //释放资源
 sqlSession.close(); 30         return dlist; 31  } 32 
 @Override 34     public List<Dept> getDeptPostList() 35  { 36         SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder(); 37         SqlSessionFactory ssf = ssfb.build(DeptMapperImpl.class. 38                 getClassLoader().getResourceAsStream("MyBatis.xml")); 39         //产生SqlSesion兑现
        SqlSession sqlSession = ssf.openSession(); 41         //进行数据的crud操作
        List<Dept> dlist = sqlSession.selectList("dept.getDeptPostList"); 43         //提交事务
 sqlSession.commit(); 45         //释放资源
 sqlSession.close(); 47         return dlist; 48  } 49 
}

1.4建立Post岗位信息表

/*
Navicat MySQL Data Transfer  3 
Source Server : MySQL  5 Source Server Version : 50715  6 Source Host : localhost:3306  7 Source Database : test  8 
Target Server Type : MYSQL 10 Target Server Version : 50715 11 File Encoding : 65001 12 
Date: 2016-12-13 20:50:00 14 */

SET FOREIGN_KEY_CHECKS=0; 17 
-- ----------------------------
-- Table structure for post
-- ----------------------------
DROP TABLE IF EXISTS `post`; 22 CREATE TABLE `post` ( 23   `pid` int(11) NOT NULL AUTO_INCREMENT, 24   `pname` varchar(255) DEFAULT NULL, 25   `pdesc` varchar(255) DEFAULT NULL, 26   `did` int(11) DEFAULT NULL, 27   PRIMARY KEY (`pid`), 28   KEY `fk_did` (`did`), 29   CONSTRAINT `fk_did` FOREIGN KEY (`did`) REFERENCES `dept` (`did`) 30 ) 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  6     </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 18  on dept.did = post.did 19     </select>
</mapper>

1.6添加测试方法

package org.guangsoft.test;  2 
import java.util.List;  4 
import org.guangsoft.entity.Dept;  6 import org.guangsoft.entity.Post;  7 import org.guangsoft.mapper.DeptMapper;  8 import org.guangsoft.mapper.impl.DeptMapperImpl;  9 import org.guangsoft.vo.DeptVo; 10 import org.junit.Test; 11 
public class TestDeptMapper 13 { 14     DeptMapper deptMapper = new DeptMapperImpl(); 15     
 @Test 17     public void testGetDeptVo() 18  { 19         List<DeptVo> dlist = deptMapper.getDeptPost(); 20         for(DeptVo deptVo : dlist) 21  { 22             System.out.println(deptVo.getDid() + 
                " " + deptVo.getDname() + deptVo.getPname()); 24  } 25  } 26     
 @Test 28     public void testGetDeptList() 29  { 30         List<Dept> dlist = deptMapper.getDeptPostList(); 31         for(Dept dept : dlist) 32  { 33  System.out.println(dept.getDname()); 34             List<Post> postList = dept.getPosts(); 35             for(Post post : postList) 36  { 37  System.out.println(post.getPname()); 38  } 39  } 40  } 41     
} 

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