SSM学习08MyBatis关联映射多对多

Posted 2021-02-14 2312947032zyk

和上一个相同还是<collection>是多对多映射，一个订单可能包含多个产品，而每个商品有可能出现在多个订单中，在数据库中这样的情况就需要一张中间表来维护。

1.在mybatis中建表：

 1 create table tb_product(
 2     id int(32) primary key auto_increment,
 3     name varchar(32),
 4     price double
 5 );
 6  
 7 insert into tb_product values(‘1‘,‘Java基础入门‘,‘44.5‘);
 8 insert into tb_product values(‘2‘,‘Java Web程序开发入门‘,‘38.5‘);
 9 insert into tb_product values(‘3‘,‘SSM框架整合实战‘,‘50‘);
10  
11 create table tb_ordersitem(
12     id int(32) primary key auto_increment,
13     orders_id int(32),
14     product_id int(32),
15     foreign key(orders_id) references tb_orders(id),
16     foreign key(product_id) references tb_product(id)
17 );
18  
19 insert into tb_ordersitem values(‘1‘,‘1‘,‘1‘);
20 insert into tb_ordersitem values(‘2‘,‘1‘,‘3‘);
21 insert into tb_ordersitem values(‘3‘,‘3‘,‘3‘);

　　　可以看出tb_ordersitem中引用了tb_prduct和tb_orders中的主键作为外键。

Product：

　　

 1 package com.zyk.po;
 2 
 3 import java.util.List;
 4 
 5 public class Product {
 6     private int id;
 7     @Override
 8     public String toString() {
 9         return "Product [id=" + id + ", name=" + name + ", price=" + price + ", orders=" + orders + "]";
10     }
11     private String name;
12     private Double price;
13     private List<Orders> orders;
14     public int getId() {
15         return id;
16     }
17     public void setId(int id) {
18         this.id = id;
19     }
20     public String getName() {
21         return name;
22     }
23     public void setName(String name) {
24         this.name = name;
25     }
26     public Double getPrice() {
27         return price;
28     }
29     public void setPrice(Double price) {
30         this.price = price;
31     }
32     public List<Orders> getOrders() {
33         return orders;
34     }
35     public void setOrders(List<Orders> orders) {
36         this.orders = orders;
37     }
38     
39     
40 }

Order：

 1 package com.zyk.po;
 2 
 3 import java.util.List;
 4 
 5 public class Orders {
 6     private int id;
 7     @Override
 8     public String toString() {
 9         return "Orders [id=" + id + ", productlist=" + productlist + ", number=" + number + "]";
10     }
11     private List<Product> productlist;
12     private String number;
13     public List<Product> getProductlist() {
14         return productlist;
15     }
16     public void setProductlist(List<Product> productlist) {
17         this.productlist = productlist;
18     }
19     
20     public int getId() {
21         return id;
22     }
23     public void setId(int id) {
24         this.id = id;
25     }
26     public String getNumber() {
27         return number;
28     }
29     public void setNumber(String number) {
30         this.number = number;
31     }
32     
33     
34 }

从两个javabean中可以看出：product中有order，order中有product

OrderMapper.xml:

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
 3      "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 4 <mapper namespace="com.itheima.mapper.OrdersMapper">
 5     <select id="findOrdersWithProduct" parameterType="Integer" resultMap="OrdersWithProductResult">
 6         select o.*,p.id as pid,p.name,p.price
 7         from tb_orders o,tb_product p,tb_ordersitem oi
 8         where oi.orders_id=o.id
 9         and oi.product_id=p.id
10         and o.id=#{id}
11     </select>
12     <resultMap type="Orders" id="OrdersWithProductResult">
13       <id property="id" column="id"/>
14       <result property="number" column="number"/>
15       <collection property="productList" ofType="Product">
16           <id property="id" column="pid"/>
17           <result property="name" column="name"/>
18           <result property="price" column="price"/>
19       </collection> 
20     </resultMap>
21 </mapper>

测试类：

1 @Test
2     public void findOrdersAndPorductTest() {
3         SqlSession session = MybatisUtils.getSession();
4         Orders orders = session.selectOne("com.itheima.mapper.OrdersMapper.findOrdersWithProduct",1);
5         System.out.println(orders);
6         //关闭SqlSession
7         session.close();
8     }

结果：