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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