一、结果映射是什么?
ResultMap
1.使用场景一
当数据库的列名和实体类的属性名不一致时,无法直接通过resultType接收查询结果.
那么我们可以是用resultMap属性应用一个结果映射,在结果映射中指定每一个列使用哪一个属性接收.
2. 使用场景二
可以通过resultMap配置对一关系和对多关系
二、如何使用结果映射?
在关联外部属性时,外部属性是一个对象就使用Association
Association:用于配置对一的关系
Property:指定本类中的属性名
Column:将自己的某一个列作为参数传入查询中
Select:调用外部查询获得数据
JavaType:本属性属于哪一种java类型
resultMap:引用其他的映射
Collection:用于配置对多的关系
Property:指定本类中的属性名
Column:将自己的某一个列作为参数传入查询中
Select:调用外部查询获得数据
ofType:本集合属性中的元素属于哪一种java类型
resultMap:引用其他的映射
在关联外部属性时,外部属性是一个集合就使用Collection
三、结果映射的使用
Sql
/*
Navicat MySQL Data Transfer
Source Server : Linux_mysql
Source Server Version : 50622
Source Host : 192.168.188.130:3306
Source Database : db_mybatis
Target Server Type : MYSQL
Target Server Version : 50622
File Encoding : 65001
Date: 2019-01-06 18:21:21
*/
SET FOREIGN_KEY_CHECKS=0;
-- ----------------------------
-- Table structure for dTable
-- ----------------------------
DROP TABLE IF EXISTS `dTable`;
CREATE TABLE `dTable` (
`dId` int(11) NOT NULL,
`dDate` datetime DEFAULT NULL,
`tId` int(11) DEFAULT NULL,
PRIMARY KEY (`dId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
-- ----------------------------
-- Table structure for tTable
-- ----------------------------
DROP TABLE IF EXISTS `tTable`;
CREATE TABLE `tTable` (
`tId` int(11) NOT NULL,
`tName` varchar(255) DEFAULT NULL,
PRIMARY KEY (`tId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
项目结构
dTableMappers.java
package mappers;
import java.util.List;
import model.dTable;
public interface dTableMappers {
List<dTable> selectAll();
}
tTableMappers.java
package mappers;
import model.tTable;
public interface tTableMappers {
public tTable selectById(Integer tId);
}
dTableMappers.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mappers.dTableMappers">
<!-- 结果映射 base -->
<resultMap id="dtableRM" type="dTable">
<id column="dId" property="dId"/>
<result column="dDate" property="dDate"/>
<result column="tId" property="tId"/>
</resultMap>
<!-- 结果映射 1-1 -->
<resultMap id="dtableRM_s" type="dTable" extends="dtableRM">
<!-- 1、点对点返回
<result column="tName" property="tTable.tname"/>
-->
<!-- 2、使用对方的 -->
<association property="tTable" resultMap="mappers.tTableMappers.tTableRM" ></association>
</resultMap>
<!-- 多表查询 -->
<select id="selectAll" resultMap="dtableRM_s">
select * from dTable t1,tTable t2 where t1.tId=t2.tId
</select>
</mapper>
tTableMappers.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mappers.tTableMappers">
<!-- 结果映射 base -->
<resultMap id="tTableRM" type="tTable">
<id column="tId" property="tId"/>
<result column="tName" property="tName"/>
</resultMap>
<!-- 结果映射 1-n -->
<resultMap type="tTable" id="tTableRM_ds" extends="tTableRM">
<!-- 1 自己写
<collection property="dTableList" ofType="dTable">
<id column="dId" property="dId"/><result column="dDate" property="dDate"/>
</collection>
-->
<!--2 使用对方的 -->
<collection property="dTableList" resultMap="mappers.dTableMappers.dtableRM"></collection>
</resultMap>
<!-- 根据ID查询（顺带，1-n） -->
<select id="selectById" parameterType="Integer" resultMap="tTableRM_ds">
select * from tTable t1 left join dTable t2 on t1.tId=t2.tId where t1.tId=#{tId}
</select>
</mapper>
dTable.java
package model;
public class dTable {
private Integer dId;
private String dDate;
private Integer tId;
private tTable tTable;
public dTable(Integer dId, String dDate, Integer tId) {
super();
this.dId = dId;
this.dDate = dDate;
this.tId = tId;
}
public dTable(String dDate, Integer tId) {
super();
this.dDate = dDate;
this.tId = tId;
}
public dTable() {
super();
}
public Integer getdId() {
return dId;
}
public void setdId(Integer dId) {
this.dId = dId;
}
public String getdDate() {
return dDate;
}
public void setdDate(String dDate) {
this.dDate = dDate;
}
public Integer gettId() {
return tId;
}
public void settId(Integer tId) {
this.tId = tId;
}
public tTable gettTable() {
return tTable;
}
public void settTable(tTable tTable) {
this.tTable = tTable;
}
@Override
public String toString() {
return "dTable [" +
"dId=" + dId + ", dDate=" + dDate +
", tId=" + tId +
", tname="+ tTable.gettName() +
" ]";
}
}
tTable.java
package model;
import java.util.List;
public class tTable {
private Integer tId;
private String tName;
private List<dTable> dTableList;
public tTable() {
super();
}
public tTable(String tname) {
super();
this.tName = tname;
}
public tTable(Integer tId, String tname) {
super();
this.tId = tId;
this.tName = tname;
}
public String gettName() {
return tName;
}
public void settName(String tName) {
this.tName = tName;
}
public Integer gettId() {
return tId;
}
public void settId(Integer tId) {
this.tId = tId;
}
public List<dTable> getdTableList() {
return dTableList;
}
public void setdTableList(List<dTable> dTableList) {
this.dTableList = dTableList;
}
@Override
public String toString() {
return "tTable ["
+ "tId=" + tId +
", tname=" + tName +
"]";
}
}
dTableTest.java
package service;
import java.util.ArrayList;
import java.util.HashMap;
import org.apache.ibatis.session.SqlSession;
import mappers.dTableMappers;
import mappers.tTableMappers;
import model.dTable;
import model.tTable;
import util.SqlSessionFactoryUtil;
public class dTableTest {
public static void main(String[] args) {
SqlSession sqlSession = SqlSessionFactoryUtil.openSession();
/** 1-n*/
// tTableMappers tTableMp = sqlSession.getMapper(tTableMappers.class);
// tTable tTable = tTableMp.selectById(1);
// System.out.println("id = "+tTable.gettId());
// System.out.println("name = "+tTable.gettName());
//
// if(tTable.getdTableList() != null)
// for (dTable d : tTable.getdTableList() ) {
// System.out.println("did = "+d.getdId());
// System.out.println("dDate = "+d.getdDate());
// }
/** 1-1*/
// dTableMappers studentMapper = sqlSession.getMapper(dTableMappers.class);
//
// for (dTable s : studentMapper.selectAll()) {
// System.out.println(s);
// }
sqlSession.commit();
}
}
SqlSessionFactoryUtil.java
package util;
import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class SqlSessionFactoryUtil {
private static SqlSessionFactory sqlSessionFactory;
public static SqlSessionFactory getSqlSessionFactory(){
if(sqlSessionFactory==null){
InputStream inputStream=null;
try{
inputStream=Resources.getResourceAsStream("mybatis-config.xml");
sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
}catch(Exception e){
e.printStackTrace();
}
}
return sqlSessionFactory;
}
public static SqlSession openSession(){
return getSqlSessionFactory().openSession();
}
}
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