MyBatis中关于resultType和resultMap的区别

MyBatis中关于resultType和resultMap的区别

时间 2014-09-17 16:53:22  CSDN博客

原文  http://blog.csdn.net/caolipeng_918/article/details/39344783

主题 MyBatis 数据库

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;
  }


  @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]