Mybatis---多对多关联映射

在数据库中，多对多的关联关系通常使用一个中间表来维护，中间表中的订单id作为外键参照订单表的id，商品id作为外键参照商品表的id。

一、项目准备

jdbc包，mybatis包，junit5(eclipse自带)

目录结构

 

二、数据库设计

其中tb_orders的id是tb_ordersitem表中orders_id的外键，tb_product的id是tb_ordersitem表中product_id的外键

 

三、贴代码

db.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1/mybaits
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

Ordrers.java

package pojo;

import java.util.List;

public class Orders {
    private Integer id;    //订单id
    private String number;//订单编号
    //关联商品集合信息
    private List productList;

    public List getProductList() {
        return productList;
    }

    public void setProductList(List productList) {
        this.productList = productList;
    }

    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 + '\'' +
                ", productList=" + productList +
                '}';
    }
}

Product.java

package pojo;

import java.util.List;

public class Product {
    private Integer id;  //商品id
    private String name; //商品名称
    private Double price;//商品单价
    private List orders; //与订单的关联属性

    public Integer getId() {
        return id;
    }

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

    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 List getOrders() {
        return orders;
    }

    public void setOrders(List orders) {
        this.orders = orders;
    }

    @Override
    public String toString() {
        return "Product{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
//                ", orders=" + orders +
                '}';
    }
}

OrdersMapper.xml

    
    
        select * from tb_orders WHERE id=#{id}
    
    
        
        
        
        
    

ProductMapper.xml

    
        SELECT * from tb_product where id IN(
            SELECT product_id FROM tb_ordersitem  WHERE orders_id = #{id}
        )
    

MybatisTest.java

package test;


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

import pojo.Orders;
import util.Utils;
public class MybatisTest {
    @Test
    public void findOrdersTest(){
        // 1、通过工具类生成SqlSession对象
        SqlSession session = Utils.getSession();
        // 2、查询id为1的订单中的商品信息
        Orders orders = session.selectOne("pojo"
                + ".OrdersMapper.findOrdersWithPorduct", 1);
        // 3、输出查询结果信息
        System.out.println(orders);
        // 4、关闭SqlSession
        session.close();
    }
}

Utils.java

package util;

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

四、测试

运行截图：