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MyBatis動(dòng)態(tài)SQL MyBatis一對(duì)多關(guān)聯(lián)查詢

MyBatis多對(duì)多關(guān)聯(lián)查詢

實(shí)際應(yīng)用中，由于多對(duì)多的關(guān)系比較復(fù)雜，會(huì)增加理解和關(guān)聯(lián)的復(fù)雜度，所以應(yīng)用較少。MyBatis 沒有實(shí)現(xiàn)多對(duì)多級(jí)聯(lián)，推薦通過兩個(gè)一對(duì)多級(jí)聯(lián)替換多對(duì)多級(jí)聯(lián)，以降低關(guān)系的復(fù)雜度，簡(jiǎn)化程序。

例如，一個(gè)訂單可以有多種商品，一種商品可以對(duì)應(yīng)多個(gè)訂單，訂單與商品就是多對(duì)多的級(jí)聯(lián)關(guān)系?？梢允褂靡粋€(gè)中間表（訂單記錄表）將多對(duì)多級(jí)聯(lián)轉(zhuǎn)換成兩個(gè)一對(duì)多的關(guān)系。

示例

下面以訂單和商品（實(shí)現(xiàn)“查詢所有訂單以及每個(gè)訂單對(duì)應(yīng)的商品信息”的功能）為例講解多對(duì)多關(guān)聯(lián)查詢。

1. 創(chuàng)建數(shù)據(jù)表

創(chuàng)建 order（訂單），product（商品）和 order_details（訂單和商品中間表），SQL 語(yǔ)句如下。

CREATE TABLE `order` (
  `oid` int(11) NOT NULL AUTO_INCREMENT,
  `ordernum` int(25) DEFAULT NULL,
  `userId` int(11) DEFAULT NULL,
  PRIMARY KEY (`oid`),
  KEY `userId` (`userId`),
  CONSTRAINT `order_ibfk_1` FOREIGN KEY (`userId`) REFERENCES `user` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

insert  into `order`(`oid`,`ordernum`,`userId`) values (1,20200107,1),(2,20200806,2),(3,20206702,3),(4,20200645,1),(5,20200711,2),(6,20200811,2),(7,20201422,3),(8,20201688,4),(9,NULL,5);

DROP TABLE IF EXISTS `orders_detail`;

CREATE TABLE `orders_detail` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `orderId` int(11) DEFAULT NULL,
  `productId` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;

insert  into `orders_detail`(`id`,`orderId`,`productId`) values (1,1,1),(2,1,2),(3,1,3),(4,2,3),(5,2,1),(6,3,2);

DROP TABLE IF EXISTS `product`;

CREATE TABLE `product` (
  `pid` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(25) DEFAULT NULL,
  `price` double DEFAULT NULL,
  PRIMARY KEY (`pid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

insert  into `product`(`pid`,`name`,`price`) values (1,'Java教程',128),(2,'C語(yǔ)言教程',138),(3,'Python教程',132.35);

2. 創(chuàng)建持久化類

Order 類代碼如下。

package net.biancheng.po;
import java.util.List;
public class Order {
    private int oid;
    private int ordernum;
    private List<Product> products;
    /*省略setter和getter方法*/
    @Override
    public String toString() {
        return "Order [id=" + oid + ", ordernum=" + ordernum + ", products=" + products + "]";
    }
}

Product 類方法如下。

package net.biancheng.po;
import java.util.List;
public class Product {
    private int pid;
    private String name;
    private Double price;
    // 多對(duì)多中的一個(gè)一對(duì)多
    private List<Order> orders;
    /*省略setter和getter方法*/
    @Override
    public String toString() {
        return "Product [id=" + pid + ", name=" + name + ", price=" + price + "]";
    }
}

3. 創(chuàng)建接口和映射文件

OrderMapper 接口代碼如下。

package net.biancheng.mapper;
import java.util.List;
import net.biancheng.po.Order;
public interface OrderMapper {
    public List<Order> selectAllOrdersAndProducts();
}

OrderMapper.xml 代碼如下。

<?xml version="1.0" encoding="UTF-8"?>
                    <!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="net.biancheng.mapper.OrderMapper">

    <resultMap type="net.biancheng.po.Order" id="orderMap">
        <id property="oid" column="oid" />
        <result property="ordernum" column="ordernum" />

        <collection property="products"
                    ofType="net.biancheng.po.Product">
            <id property="pid" column="pid" />
            <result property="name" column="name" />
            <result property="price" column="price" />
        </collection>
    </resultMap>

    <select id="selectAllOrdersAndProducts" parameterType="Integer"
            resultMap="orderMap">
        SELECT o.oid,o.`ordernum`,p.`pid`,p.`name`,p.`price` FROM
        `order` o
        INNER JOIN orders_detail od ON o.oid=od.`orderId`
        INNER JOIN
        product p
        ON p.pid = od.`productId`
    </select>

</mapper>

4. 創(chuàng)建測(cè)試類

測(cè)試類代碼如下。

package net.biancheng.test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import net.biancheng.mapper.OrderMapper;
import net.biancheng.po.Order;
public class Test {
    public static void main(String[] args) throws IOException {
        InputStream config = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(config);
        SqlSession ss = ssf.openSession();
        List<Order> orderList = ss.getMapper(OrderMapper.class).selectAllOrdersAndProducts();
        for (Order or : orderList) {
            System.out.println(or);
        }
    }
}

運(yùn)行結(jié)果如下。

DEBUG [main] - ==>  Preparing: SELECT o.oid,o.`ordernum`,p.`pid`,p.`name`,p.`price` FROM `order` o INNER JOIN orders_detail od ON o.oid=od.`orderId` INNER JOIN product p ON p.pid = od.`productId`
DEBUG [main] - ==> Parameters:
DEBUG [main] - <==      Total: 6
Order [id=1, ordernum=20200107, products=[Product [id=1, name=Java教程, price=128.0], Product [id=2, name=C語(yǔ)言教程, price=138.0], Product [id=3, name=Python教程, price=132.35]]]
Order [id=2, ordernum=20200806, products=[Product [id=3, name=Python教程, price=132.35], Product [id=1, name=Java教程, price=128.0]]]
Order [id=3, ordernum=20206702, products=[Product [id=2, name=C語(yǔ)言教程, price=138.0]]]

MyBatis動(dòng)態(tài)SQL MyBatis一對(duì)多關(guān)聯(lián)查詢