MyBatis实现多对一

偏执的太偏执、 2022-04-15 04:24 164阅读 0赞

**在本人写的一对多的基础上继续修改，点击下面的连接即可跳转到一对多：**  
[https://blog.csdn.net/qq\_43254488/article/details/84316244][https_blog.csdn.net_qq_43254488_article_details_84316244]  
**第一个修改的地方：修改实体映射文件：**  
person.xml配置文件（下边代码的解释在一对多中有注解解释）：

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE mapper PUBLIC "mybatis-3-mapper" "mybatis-3-mapper.dtd" >
    <mapper namespace="com.zhiyuan.Bean">
    	<resultMap type="food" id="aa">
    		<result property="id" column="id"/>
    		<result property="p_id" column="p_id"/>
    		<result property="fname" column="fname"/>
    		<result property="fkouwei" column="fkouwei"/>
    		<association property="person" javaType="person">
    			<result property="id" column="id"/>
    			<result property="name" column="name"/>
    			<result property="sex" column="sex"/>
    		</association>
    	</resultMap>
    	<select id="GetID" parameterType="String" resultMap="aa">
    		select * from person,food where person.id=food.p_id and food.fkouwei=#{fkouwei}
    	</select>
    </mapper>

**第二个修改的地方：修改测试类：**  
Text类：

package com.zhiyuan.Text;
    
    import java.io.IOException;
    import java.io.Reader;
    import java.util.List;
    
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    
    import com.zhiyuan.Bean.Food;
    import com.zhiyuan.Bean.Person;
    
    public class Text {
    
    	public static void main(String[] args) throws IOException {
    		Reader reader = Resources.getResourceAsReader("config.xml");
    		//通过Resources类调用getResourceAsReader方法来获取 config主配置文件并用Reader来进行接收
    		SqlSessionFactory session = new SqlSessionFactoryBuilder().build(reader);//创建工厂回话
    		List<Food> list= session.openSession().selectList("com.zhiyuan.Bean.GetID","甜");
    		//openSession用来创建Sqlsession，selectList用来查询一条或多条记录
    		for (Food food : list) {
    			System.out.println("ID:"+food.getId()+"  P_Id:"+food.getP_id()+"  食物名:"+food.getFname()+"  口味:"+food.getFkouwei());
    			Person person= food.getPerson();
    			System.out.println("ID:"+person.getId()+"  姓名:"+person.getName()+"  性别:"+person.getSex());
    		}
    		//上边是查询一条或多条语句，下边是查询一条语句
    //		Food food= session.openSession().selectOne("com.zhiyuan.Bean.GetID",1);
    		//如果需要用selectOne来接收，需要在person.xml文件中改两个地方：
    		//1.将parameterType="String"中的String修改为int，因为1是int类型。
    		//2.将查询语句中的food.fkouwei=#{fkouwei}中的food.fkouwei改为food.id因为之前是根据口味来查询，现在是根据id来查询
    //		System.out.println("ID:"+food.getId()+"  P_Id:"+food.getP_id()+"  食物名:"+food.getFname()+"  口味:"+food.getFkouwei());
    //		Person person = food.getPerson();
    //		System.out.println("ID:"+person.getId()+"  姓名:"+person.getName()+"  性别:"+person.getSex());
    	}
    
    }

**运行结果：**  
用selectList查询出来的结果为下图所示  
![在这里插入图片描述][20181122083858852.jpg]  
用selectOne查询出来的结果为下图所示  
![在这里插入图片描述][20181122084109858.jpg]

[https_blog.csdn.net_qq_43254488_article_details_84316244]: https://blog.csdn.net/qq_43254488/article/details/84316244
[20181122083858852.jpg]: /images/20220415/318aa89e6a4f491ba358af62d8d3646a.png
[20181122084109858.jpg]: /images/20220415/ef983309152a44dfb1987abe099cafde.png