MyBatis中关于resultType和resultMap的区别

MyBatis中关于resultType和resultMap的区别

  MyBatis中在查询进行select映射的时候，返回类型可以用resultType，也可以用resultMap，resultType是直接表示返回类型的(对应着我们的model对象中的实体)，而resultMap则是对外部ResultMap的引用(提前定义了db和model之间的隐射key-->value关系)，但是resultType跟resultMap不能同时存在。
  在MyBatis进行查询映射时，其实查询出来的每一个属性都是放在一个对应的Map里面的，其中键是属性名，值则是其对应的值。
  ①当提供的返回类型属性是resultType时，MyBatis会将Map里面的键值对取出赋给resultType所指定的对象对应的属性。所以其实MyBatis的每一个查询映射的返回类型都是ResultMap，只是当提供的返回类型属性是resultType的时候，MyBatis对自动的给把对应的值赋给resultType所指定对象的属性。
  ②当提供的返回类型是resultMap时，因为Map不能很好表示领域模型，就需要自己再进一步的把它转化为对应的对象，这常常在复杂查询中很有作用。

  下面给出一个例子说明两者的使用差别:

package com.clark.model;import java.util.Date;public class Goods {private Integer id;private Integer cateId;private String name;private double price;private String description;private Integer orderNo;private Date updateTime;public Goods(){}public Goods(Integer id, Integer cateId, String name, double price,String description, Integer orderNo, Date updateTime) {super();this.id = id;this.cateId = cateId;this.name = name;this.price = price;this.description = description;this.orderNo = orderNo;this.updateTime = updateTime;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public Integer getCateId() {return cateId;}public void setCateId(Integer cateId) {this.cateId = cateId;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}public Integer getOrderNo() {return orderNo;}public void setOrderNo(Integer orderNo) {this.orderNo = orderNo;}public Date getTimeStamp() {return updateTime;}public void setTimeStamp(Date updateTime) {this.updateTime = updateTime;}@Overridepublic String toString() {return "[goods include:Id="+this.getId()+",name="+this.getName()+",orderNo="+this.getOrderNo()+",cateId="+this.getCateId()+",updateTime="+this.getTimeStamp()+"]";}}

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><typeAliases><!-- give a alias for model --><typeAlias alias="goods" type="com.clark.model.Goods"></typeAlias></typeAliases><environments default="development"><environment id="development"><transactionManager type="JDBC" /><dataSource type="POOLED"><property name="driver" value="oracle.jdbc.driver.OracleDriver" /><property name="url" value="jdbc:oracle:thin:@172.30.0.125:1521:oradb01" /><property name="username" value="settlement" /><property name="password" value="settlement" /></dataSource></environment></environments><mappers><mapper resource="com/clark/model/goodsMapper.xml" /></mappers></configuration></span>

<?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="clark"><resultMap type="com.clark.model.Goods" id="t_good"><id column="id" property="id"/><result column="cate_id" property="cateId"/><result column="name" property="name"/><result column="price" property="price"/><result column="description" property="description"/><result column="order_no" property="orderNo"/><result column="update_time" property="updateTime"/></resultMap><!--resultMap 和   resultType的使用区别--><select id="selectGoodById" parameterType="int" resultType="goods">select id,cate_id,name,price,description,order_no,update_time from goods where id = #{id}</select><select id="selectAllGoods" resultMap="t_good">select id,cate_id,name,price,description,order_no,update_time from goods</select><insert id="insertGood" parameterType="goods">insert into goods(id,cate_id,name,price,description,order_no,update_time)  values(#{id},#{cateId},#{name},#{price},#{description},#{orderNo},#{updateTime})</insert></mapper>

package com.clark.mybatis;import java.io.IOException;import java.io.Reader;import java.util.List;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import com.clark.model.Goods;public class TestGoods {public static void main(String[] args) {String resource = "configuration.xml";try {Reader reader = Resources.getResourceAsReader(resource);SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);SqlSession session = sessionFactory.openSession();</span>

<span style="font-size:18px;"><span style="white-space:pre"></span>//使用resultType的情况Goods goods = (Goods)session.selectOne("clark.selectGoodById", 4);System.out.println(goods.toString());</span>

<span style="font-size:18px;"><span style="white-space:pre"></span>//使用resultMap的情况List<Goods> gs = session.selectList("clark.selectAllGoods");for (Goods goods2 : gs) {System.out.println(goods2.toString());}//Goods goods = new Goods(4, 12, "clark", 12.30, "test is ok", 5, new Date());//session.insert("clark.insertGood", goods);//session.commit();} catch (IOException e) {e.printStackTrace();}}}

结果输出为:

<span style="color:#cc0000;">[goods include:Id=4,name=clark,orderNo=null,cateId=null,updateTime=null]---使用resultType的结果</span>

<span style="color:#33ff33;">-------使用resultMap的结果-----------------</span>

[goods include:Id=4,name=clark,orderNo=5,cateId=12,updateTime=Wed Sep 17 15:29:58 CST 2014][goods include:Id=1,name=诺基亚N85,orderNo=1,cateId=1,updateTime=Wed Sep 17 13:52:51 CST 2014]
[goods include:Id=2,name=金立 A30,orderNo=2,cateId=1,updateTime=Wed Sep 17 13:53:11 CST 2014][goods include:Id=3,name=金立 A30,orderNo=3,cateId=2,updateTime=Wed Sep 17 15:07:38 CST 2014]