【SSM - Mybatis篇08】多对对多关联查询

案例描述

  多对多关联，其实就是两个一对多相互关联实现。MyBatis并没有提供多对多关联的实现，还是用resultMap的collection实现。
  订单和产品之间是多对多的关系，一个订单可以有多个产品，一个产品可以有多份订单，创建订单表orders、产品表product、和中间表order_product。

1. 创建orders、product表和中间表order_product

-- ----------------------------
-- 创建订单表orders
-- ----------------------------
CREATE TABLE `orders` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `description` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

INSERT INTO `orders` VALUES ('1', '一季度采购订单');
INSERT INTO `orders` VALUES ('2', '二季度采购订单');
INSERT INTO `orders` VALUES ('3', '三季度采购订单');
INSERT INTO `orders` VALUES ('4', '四季度采购订单');

-- ----------------------------
-- 创建产品表product
-- ----------------------------
CREATE TABLE `product` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(100) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;

INSERT INTO `product` VALUES ('1', '医用口罩');
INSERT INTO `product` VALUES ('2', 'KN95口罩');
INSERT INTO `product` VALUES ('3', '笔记本电脑');
INSERT INTO `product` VALUES ('4', '数码相机');
INSERT INTO `product` VALUES ('5', '冰箱');
INSERT INTO `product` VALUES ('6', '空调');

	-- ----------------------------
-- 创建中间表 order_product，ordersId映射orders表的主键id，productId映射product表的主键id
-- ----------------------------
DROP TABLE IF EXISTS `orders_product`;
CREATE TABLE `orders_product` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `ordersId` int(11) DEFAULT NULL,
  `productId` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `FK_orders` (`ordersId`),
  KEY `FK_product` (`productId`),
  CONSTRAINT `FK_orders` FOREIGN KEY (`ordersId`) REFERENCES `orders` (`id`),
  CONSTRAINT `FK_product` FOREIGN KEY (`productId`) REFERENCES `product` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

INSERT INTO `orders_product` VALUES ('1', '1', '1');
INSERT INTO `orders_product` VALUES ('2', '1', '2');
INSERT INTO `orders_product` VALUES ('3', '1', '3');
INSERT INTO `orders_product` VALUES ('4', '2', '4');
INSERT INTO `orders_product` VALUES ('5', '2', '3');
INSERT INTO `orders_product` VALUES ('6', '1', '6');
INSERT INTO `orders_product` VALUES ('7', '2', '5');

2. 创建javabean对象

//orders表
public class Order {
    
    
    private Integer id;
    private String description;
    private List<Product> productList;
    //省略getter/setter方法
}
//product表
public class Product {
    
    
    private Integer id;
    private String name;
}

3. 创建dao层

@Repository
public interface OrderMapper {
    
    
// 通过order订单的id查询订单，并输出该订单的所有产品product
    Order getOrderById(int i);
}

4. 创建连接数据库的属性文件db.properties(键值对形式)

jdbc.driver = com.mysql.jdbc.Driver
jdbc.url = jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=UTF-8
jdbc.username = root
jdbc.password = 861221293

5. spring整合MyBatis，核心配置文件applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mybatis="http://mybatis.org/schema/mybatis-spring" xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://mybatis.org/schema/mybatis-spring http://mybatis.org/schema/mybatis-spring.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd">


    <!--1. 引入jdbc的属性文件，在配置中通过占位使用 -->
    <context:property-placeholder location="classpath*:db.properties" />

    <!--2. <context:component-scan>扫描包中注解所标注的类(@Component、@Service、@Controller、@Repository) -->
    <context:component-scan base-package="com.xgf.correlation.many_to_many"/>

    <!--3. 由spring管理    配置数据源数据库连接(从jdbc属性文件中读取参数) -->
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="username" value="${jdbc.username}"/>
        <property name="password" value="${jdbc.password}"/>
        <property name="url" value="${jdbc.url}"/>
        <property name="driverClassName" value="${jdbc.driver}"/>
    </bean>

    <!--  通过spring来管理Mybatis的sqlSessionFactory对象创建  -->
    <!--4. 通过完全限定名匹配查找  创建SqlSessionFactoryBean  -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <!-- 5. mybatis提供的一个注解扫描标签（搜索映射器 Mapper 接口），通过自动扫描注解的机制，创建每个dao接口定义的bean  -->
    <mybatis:scan base-package="com.xgf.correlation.many_to_many"/>

</beans>

6. 创建映射文件mapper.xml

OrderMapper.xml

<?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">
<!--
    oid pid是查询select语句起的别名
-->
<mapper namespace="com.xgf.correlation.many_to_many.dao.OrderMapper">

    <resultMap id="orderMap" type="com.xgf.correlation.many_to_many.bean.Order">
        <id column="oid" property="id"/>
        <result property="description" column="description"/>
        <collection property="productList" ofType="com.xgf.correlation.many_to_many.bean.Product">
            <id column="pid" property="id"/>
            <result property="name" column="name"/>
        </collection>
    </resultMap>

    <select id="getOrderById" parameterType="int" resultMap="orderMap">
           select o.id oid,o.description,p.id pid,p.name
            from orders o left outer join orders_product op on o.id = op.ordersId
                          left outer join product p on p.id = op.productId
            where o.id = #{id}

    </select>
    
</mapper>

7. 创建测试类

//测试类
public class TestManyToMany {
    
    

    private static ApplicationContext applicationContext = null;
    private static OrderMapper orderMapper = null;

    //静态代码块 只加载一次
    static {
    
    
        //加载配置文件
        applicationContext = new ClassPathXmlApplicationContext("com/xgf/correlation/many_to_many/config/applicationContext.xml");
        //获取bean的两种方式
        // 1.类名首字母小写
//        studentMapper = (StudentMapper) applicationContext.getBean("orderMapper");
        // 2.类.class
        orderMapper = (OrderMapper) applicationContext.getBean(OrderMapper.class);
    }

     通过order订单的id查询订单，并输出该订单的所有产品product
    @Test
    public void test01(){
    
    
        System.out.println("===一条SQL语句查询  查找id为1的order和他的product列表：===");
        Order order = orderMapper.getOrderById(1);
        System.out.println(order);
    }
}

运行结果

Order{id=1, description=‘一季度采购订单’, productList=[Product{id=1, name=‘医用口罩’}, Product{id=2, name=‘KN95口罩’}, Product{id=3, name=‘笔记本电脑’}, Product{id=6, name=‘空调’}]}