Mybatis---一对多关联映射

一个客户可以有多个订单，而一个订单只能对应一个客户，一对多映射的关键就是在“多”的一方添加“一”的主键为外键

一、项目准备

可以查看我上一篇博客的介绍

传送门：https://blog.csdn.net/Wwt819635881/article/details/89811209

目录结构：

二、设计数据库

两个表tb_user和tb_orders,其中user_id是tb_orders的外键，并插入部分数据。

三、贴代码

db.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1/mybatisTest3
jdbc.username=root
jdbc.password=1234

log4j.properties

# Global logging configuration
log4j.rootLogger=ERROR, stdout
# MyBatis logging configuration...
log4j.logger.com.ssm=DEBUG
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

Orders.java

package pojo;

public class Orders {
	 private Integer id;    //订单id
	 private String number;//订单编号
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getNumber() {
		return number;
	}
	public void setNumber(String number) {
		this.number = number;
	}
	@Override
	public String toString() {
		return "Orders [id=" + id + ", number=" + number + "]";
	}
	 
}

User.java

package pojo;

import java.util.List;

public class User {
    private Integer id;                 // 用户编号
    private String username;           // 用户姓名
    private String address;            // 用户地址
    private List ordersList; //用户关联的订单

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public List getOrdersList() {
        return ordersList;
    }

    public void setOrdersList(List ordersList) {
        this.ordersList = ordersList;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", ordersList=" + ordersList +
                '}';
    }
}

OrdersMapper.xml

	
	
		select*from tb_orders where id = #{id}
		

UserMapper.xml

    
    
        SELECT u.*,o.id as orders_id,o.number
        from tb_user u,tb_orders o
        WHERE u.id=o.user_id
          and u.id=#{id}
    
    
        
        
        
        
        
            
            
        
    

MybatisTest.java

package test;


import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import pojo.User;
import utils.Utils;
public class MybatisTest {
	@Test
    public void findUserTest() {
        // 1、通过工具类生成SqlSession对象
        SqlSession session = Utils.getSession();
        // 2、查询id为1的用户信息
        User user = session.selectOne("pojo"
                + ".UserMapper.findUserWithOrders", 1);
        // 3、输出查询结果信息
        System.out.println(user);
        // 4、关闭SqlSession
        session.close();
    }
}

Utils.java

package utils;

import java.io.Reader;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
/**
 * 工具类
 */
public class Utils {
    private static SqlSessionFactory sqlSessionFactory = null;
    // 初始化SqlSessionFactory对象
    static {
        try {
            // 使用MyBatis提供的Resources类加载MyBatis的配置文件
            Reader reader =
                    Resources.getResourceAsReader("mybatis-config.xml");
            // 构建SqlSessionFactory工厂
            sqlSessionFactory =
                    new SqlSessionFactoryBuilder().build(reader);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    // 获取SqlSession对象的静态方法
    public static SqlSession getSession() {
        return sqlSessionFactory.openSession();
    }
}

mybatis-config.xml

运行截图：

我们可以看到，“用户”亚索有两个“订单”，当查询亚索的id时，对应的订单也打印出来了