0051 MyBatis关联映射--多对多关系

用户与订单时一对多关系，再加上商品信息的话，订单与商品之间就是多对多关系了

DROP DATABASE IF EXISTS testdb;
USE testdb;
/*用户表，记录用户信息；用户与订单为一对多关系：一个用户可拥有多个订单*/
DROP TABLE IF EXISTS `tb_user`;
CREATE TABLE tb_user(
    id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(18),
    loginname VARCHAR(18),
    PASSWORD VARCHAR(18),
    phone VARCHAR(18),
    address VARCHAR(18)
);

INSERT INTO tb_user(username,loginname,PASSWORD,phone,address) VALUES('杰克','jack','123456','13920001616','广州');

/*商品信息表；商品与订单为多对多关系：一个订单可有多个商品，一个商品也可出现在多个订单中*/
DROP TABLE IF EXISTS `tb_article`;
CREATE TABLE tb_article(
    id INT PRIMARY KEY AUTO_INCREMENT,
    NAME VARCHAR(32),
    price DOUBLE,
    remark VARCHAR(18)
);

INSERT INTO tb_article(NAME,price,remark) VALUES('疯狂Java讲义',108.9,'李刚老师经典着作');
INSERT INTO tb_article(NAME,price,remark) VALUES('疯狂Android讲义',99.9,'李刚老师经典着作');
INSERT INTO tb_article(NAME,price,remark) VALUES('疯狂iOS讲义',89.9,'李刚老师经典着作');
INSERT INTO tb_article(NAME,price,remark) VALUES('SpringMVC+MyBatis企业开发',69.9,'肖文吉老师经典着作');

/*订单表，记录订单编号，总金额，所属用户的id；订单与用户为多对一关系，与商品为多对多关系*/
DROP TABLE IF EXISTS `tb_order`;
CREATE TABLE tb_order(
    id INT PRIMARY KEY AUTO_INCREMENT,
    CODE VARCHAR(32),
    total DOUBLE,
    user_id INT,
    FOREIGN KEY (user_id) REFERENCES tb_user(id)
);

INSERT INTO tb_order(CODE,total,user_id) VALUES('6aa3fa359ff14619b77fab5990940a2d',388.6,1);
INSERT INTO tb_order(CODE,total,user_id) VALUES('6aa3fa359ff14619b77fab5990940b3c',217.8,1);

/*中间表，用于记录订单对应的商品id*/
DROP TABLE IF EXISTS `tb_item`;
CREATE TABLE tb_item(
    order_id INT,
    article_id INT,
    amount INT,
    PRIMARY KEY(order_id,article_id),
    FOREIGN KEY (order_id) REFERENCES tb_order(id),
    FOREIGN KEY (article_id) REFERENCES tb_article(id)
);

INSERT INTO tb_item(order_id,article_id,amount) VALUES(1,1,1);
INSERT INTO tb_item(order_id,article_id,amount) VALUES(1,2,1);
INSERT INTO tb_item(order_id,article_id,amount) VALUES(1,3,2);
INSERT INTO tb_item(order_id,article_id,amount) VALUES(2,4,2);
INSERT INTO tb_item(order_id,article_id,amount) VALUES(2,1,1);

实体类User

package net.sonng.manytomany;

import java.util.List;

public class User {
    private int id;
    private String username;
    private String loginname;
    private String password;
    private String phone;
    private String address;
    private List<Order> orders; //用户与订单：一对多关系，一个用户可有多个订单
    //...... 
}

实体类Order

package net.sonng.manytomany;

import java.util.List;

public class Order {
    private int id;
    private String code;
    private double total;
    private int user_id;
    private User user;              //一个订单只属于一个用户
    private List<Article> articles; //订单与商品：多对多关系，一个订单可包含多个商品，一个商品也可以出现在多个订单中
    //..... 
}

实体类Article

package net.sonng.manytomany;

import java.util.List;

public class Article {
    private int id;
    private String name;
    private double price;
    private String remark;
    private List<Order> orders;  //商品与订单：多对多关系
    //.....
}

根据用户id查询用户信息，并将其所有订单信息一并查询出来

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//ibatis.apache.org//DTDMapper 3.0//EN" "http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">
<mapper namespace="net.sonng.manytomany.UserDao">
    
    <select id="selectUserById" parameterType="int" resultMap="userMap">
        SELECT * FROM tb_user WHERE id=#{user_id}
    </select>

    <resultMap id="userMap" type="net.sonng.manytomany.User">
        <id property="id" column="id" />
        <result property="username" column="username" />
        <result property="loginname" column="loginname" />
        <result property="password" column="password" />
        <result property="phone" column="phone" />
        <result property="address" column="address" />
        <!-- 用户与订单一对多关系，用collection -->
        <collection property="orders" column="id" javaType="ArrayList" ofType="net.sonng.manytomany.Order" select="net.sonng.manytomany.OrderDao.selectOrderByUserId" >
            <id property="id" column="id" />
            <result property="code" column="code" />
            <result property="total" column="total" />
        </collection>
    </resultMap>
    
</mapper>

根据订单id查询订单信息，一并将其所属的用户信息和包含的商品信息查询出来

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//ibatis.apache.org//DTDMapper 3.0//EN" "http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">
<mapper namespace="net.sonng.manytomany.OrderDao">

    <select id="selectOrderByUserId" parameterType="int" resultType="net.sonng.manytomany.Order" >
        SELECT * FROM tb_order WHERE user_id=#{user_id} 
    </select>

    <select id="selectOrderById" parameterType="int" resultMap="orderMap">
        SELECT u.*,o.id AS oid,code,total,user_id FROM tb_order o,tb_user u WHERE o.user_id=u.id AND o.id=#{order_id}
    </select>
    
    <resultMap type="net.sonng.manytomany.Order" id="orderMap" >
        <id property="id" column="id" />
        <result property="code" column="code" />
        <result property="total" column="total" />
        <association property="user" javaType="net.sonng.manytomany.User">
            <id property="id" column="id" />
            <result property="username" column="username" />
            <result property="loginname" column="loginname" />
            <result property="password" column="password" />
            <result property="phone" column="phone" />
            <result property="address" column="address" />
        </association>
        <collection property="articles" column="id" javaType="ArrayList" ofType="net.sonng.manytomany.Article" select="net.sonng.manytomany.ArticleDao.selectArticleByOrderId" >
            <id property="id" column="id" />
            <result property="name" column="name" />
            <result property="price" column="price" />
            <result property="remark" column="remark" />
        </collection>
    </resultMap>
</mapper>

根据订单id，先从中间表item中查询其包含的商品id，再查询这些商品的信息

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//ibatis.apache.org//DTDMapper 3.0//EN" "http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">
<mapper namespace="net.sonng.manytomany.ArticleDao">
    
    <select id="selectArticleByOrderId" parameterType="int" resultType="net.sonng.manytomany.Article">
        SELECT * FROM tb_article WHERE id IN (SELECT article_id FROM tb_item WHERE order_id=#{order_id})
    </select>

</mapper>

测试类

package net.sonng.test;

import java.util.List;

import net.sonng.manytomany.Article;
import net.sonng.manytomany.ArticleDao;
import net.sonng.manytomany.Order;
import net.sonng.manytomany.OrderDao;
import net.sonng.manytomany.User;
import net.sonng.manytomany.UserDao;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args){
        ApplicationContext ac=new ClassPathXmlApplicationContext("ac.xml");
        
        System.out.println("测试用户查询：根据用户id查询用户信息及其订单信息");
        UserDao userDao=ac.getBean("userDao",UserDao.class);
        User user=userDao.selectUserById(1);
        System.out.println("------用户信息------");
        System.out.println(user);
        List<Order> orders=user.getOrders();
        System.out.println("------该用户下的订单信息------");
        for (Order order:orders){
            System.out.println(order);
        }
        
        System.out.println("测试订单查询：根据订单id查询订单信息，所属用户信息，订单包含的商品信息");
        OrderDao orderDao=ac.getBean("orderDao",OrderDao.class);
        Order order=orderDao.selectOrderById(2);
        System.out.println("------订单信息------");
        System.out.println(order);
        System.out.println("------订单所属用户信息------");
        System.out.println(order.getUser());
        List<Article> articles=order.getArticles();
        System.out.println("------订单包含的商品信息------");
        for (Article article:articles) {
            System.out.println(article);
        }
    }
}

输出：

测试用户查询：根据用户id查询用户信息及其订单信息
------用户信息------
User [id=1, username=杰克, loginname=jack, password=123456, phone=13920001616, address=广州]
------该用户下的订单信息------
Order [id=1, code=6aa3fa359ff14619b77fab5990940a2d, total=388.6, user_id=1]
Order [id=2, code=6aa3fa359ff14619b77fab5990940b3c, total=217.8, user_id=1]
测试订单查询：根据订单id查询订单信息，所属用户信息，订单包含的商品信息
------订单信息------
Order [id=1, code=6aa3fa359ff14619b77fab5990940b3c, total=217.8, user_id=0]
------订单所属用户信息------
User [id=1, username=杰克, loginname=jack, password=123456, phone=13920001616, address=广州]
------订单包含的商品信息------
Article [id=1, name=疯狂Java讲义, price=108.9, remark=李刚老师经典着作]
Article [id=2, name=疯狂Android讲义, price=99.9, remark=李刚老师经典着作]
Article [id=3, name=疯狂iOS讲义, price=89.9, remark=李刚老师经典着作]