MyBatis有关resultType和resultMap差异

  MyBatis中在查询进行select映射的时候，返回类型能够用resultType，也能够用resultMap。resultType是直接表示返回类型的(相应着我们的model对象中的实体)，而resultMap则是对外部ResultMap的引用(预定义了db和model之间的隐射key-->value关系)，可是resultType跟resultMap不能同一时候存在。

在MyBatis进行查询映射时。事实上查询出来的每个属性都是放在一个相应的Map里面的。当中键是属性名，值则是其相应的值。

  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所指定的对象相应的属性。所以事实上MyBatis的每个查询映射的返回类型都是ResultMap，仅仅是当提供的返回类型属性是resultType的时候，MyBatis对自己主动的给把相应的值赋给resultType所指定对象的属性。

  ②当提供的返回类型是resultMap时，由于Map不能非常好表示领域模型，就须要自己再进一步的把它转化为相应的对象，这经常在复杂查询中非常有作用。

  以下给出一个样例说明两者的使用区别:

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;

	}

	@Override

	public 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的使用差别-->

	<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]

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