4.MyBatis映射

需求分析

1.订单商品数据模型
(1).表
用户表user:记录了购买商品的用户信息
订单表orders:记录了用户所创建的订单信息
订单明细表orderdetail:记录了订单的详细信息
商品表item:记录了商品详细信息

(2).表与表之间的业务关系
在分析表与表之间的业务关系时，需要建立在某个具体业务的场景，先分析数据库级别之间有关系的表之间的业务关系。

user —> orders:一个用户可以创建多个订单，一对多
orders —> user:一个订单只由一个用户创建，一对一
orders —> orderdetail:一个订单可以包括多个订单明细，一对多，因为一个订单可以购买多个商品，每个商品的购买信息存在orderdetail
orderdetail —> orders:一个订单明细只能包括在一个订单中，一对一
orderdetail —> itesms:一个订单明细只对应一个商品信息，一对一
items –> orderdetail:一个商品可以包括在多个订单明细，一对多

2.数据准备
(1).订单表orders

CREATE TABLE `orders` (
	`order_id` int(11) NOT NULL,
	`user_id` int(11) NOT NULL,
	`order_no` varchar(100) NOT NULL,
	`note` varchar(100) NOT NULL,
	`create_time` datetime(6) NOT NULL,
  	PRIMARY KEY (`order_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert into orders values(1,1,"20221207173000000001","Steven买了一台电脑和两部手机","2022-12-07 17:30:00");
insert into orders values(2,2,"20221207173500000002","Sherry买了一部手机和两台电脑","2022-12-07 17:35:00");

(2).订单详情表orderdetail

CREATE TABLE `orderdetail` (
	`order_detail_id` int(11) NOT NULL,
	`order_id` int(11) NOT NULL,
	`item_id` int(11) NOT NULL,
	`item_num` int(11) NOT NULL,
	`create_time` datetime(6) NOT NULL,
  	PRIMARY KEY (`order_detail_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert into orderdetail values(1,1,1,1,"2022-12-07 17:30:00");
insert into orderdetail values(2,1,2,2,"2022-12-07 17:30:00");
insert into orderdetail values(3,2,1,2,"2022-12-07 17:35:00");
insert into orderdetail values(4,2,2,1,"2022-12-07 17:35:00");

(3).商品表item

CREATE TABLE `item` (
	`item_id` int(11) NOT NULL,
	`item_name` varchar(100) NOT NULL,
	`item_price` decimal(6,2) NOT NULL,
	`create_time` datetime(6) NOT NULL,
  	PRIMARY KEY (`item_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert into item values(1,"电脑",9999.99,"2022-12-07 00:00:00");
insert into item values(2,"手机",6666.66,"2022-12-07 00:00:00");

关联查询

1.一对一(查询所有订单信息，关联查询下单用户信息)
(1).修改SQL映射文件
在mybatis.xml文件中，修改SQL映射文件，具体代码如下。

<!-- 2.在全局配置文件中加载SQL映射文件 -->
<mappers>
    <mapper resource="mapper/OrdersUserMapper.xml"/>
</mappers>

(2).编写po类
在po目录下新建Orders类，具体代码如下。

public class Orders {
    private Integer orderId;

    private Integer userId;

    private String orderNo;

    private String note;

    private Date createTime;

    //get和set方法......
}

在bo目录下新建OrdersUser类，具体代码如下。

public class OrdersUser extends Orders {
    private User user;

    //get和set方法......
}

(3).编写Mapper接口
并在mapper目录下新建OrdersUserMapper接口，具体代码如下。

public interface OrdersUserMapper {
    List<OrdersUser> findOrdersUser();
}

(4).编写SQL映射
在mapper目录下新建OrdersUserMapper.xml文件，具体代码如下。

<?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="com.steven.mapper.OrdersUserMapper">
    <resultMap  id="ordersUserMap" type="com.steven.bo.OrdersUser">
        <id column="order_id" property="orderId"/>
        <result column="order_no" property="orderNo"/>
        <result column="note" property="note"/>
        <association javaType="com.steven.po.User" property="user">
            <id column="user_id" property="id"/>
            <result column="username" property="username"/>
            <result column="address" property="address" />
        </association>
    </resultMap>

    <select id="findOrdersUser" resultMap="ordersUserMap">
	    SELECT a.*,b.username,b.address
	    FROM orders as a join user as b
	    on a.user_id = b.id
	</select>
</mapper>

(5).编写测试类
Test类中调整获取Mapper和业务操作代码，具体代码如下。

public class Test {
    public static void main(String[] args) throws Exception {
        //1.获取MyBatis全局配置文件流
        String resource = "config/mybatis.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //2.根据MyBatis配置信息创建会话工厂
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //3.获取会话对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //4.获取Mapper
        OrdersUserMapper ordersUserMapper = sqlSession.getMapper(OrdersUserMapper.class);
        //5.业务操作
        List<OrdersUser> ordersUserList = ordersUserMapper.findOrdersUser();
        Iterator<OrdersUser> iterator = ordersUserList.iterator();
        while (iterator.hasNext()) {
            OrdersUser ordersUser = iterator.next();
            System.out.println("orderNo:" + ordersUser.getOrderNo());
            System.out.println("note:" + ordersUser.getNote());
            System.out.println("username:" + ordersUser.getUser().getUsername());
            System.out.println("address:" + ordersUser.getUser().getAddress());
            System.out.println();
        }
        sqlSession.close();
    }
}

orderNo:20221207173000000001
note:Steven买了一台电脑和两部手机
username:steven
address:nanjing

orderNo:20221207173500000002
note:Sherry买了一部手机和两台电脑
username:sherry
address:taizhou

(6).工程目录
在这里插入图片描述

2.一对多(查询所有订单信息关联查询订单明细信息)
(1).修改SQL映射文件
在mybatis.xml文件中，修改SQL映射文件，具体代码如下。

<!-- 2.在全局配置文件中加载SQL映射文件 -->
<mappers>
    <mapper resource="mapper/OrdersOrderDetailMapper.xml"/>
</mappers>

(2).编写po类
在po目录下新建Orders类，具体代码如下。

public class OrderDetail {
    private Integer orderDetailId;

    private Integer orderId;

    private Integer itemId;

    private Integer itemNum;

    private Date createTime;

    //get和set方法......
}

在bo目录下新建OrdersOrderDetail类，具体代码如下。

public class OrdersUser extends Orders {
    List<OrderDetail> orderDetailList;

    //get和set方法......
}

(3).编写Mapper接口
并在mapper目录下新建OrdersOrderDetailMapper接口，具体代码如下。

public interface OrdersUserMapper {
    List<OrdersOrderDetail> getOrdersOrderDetail();
}

(4).编写SQL映射
在mapper目录下新建OrdersOrderDetailMapper.xml文件，具体代码如下。

<?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="com.steven.mapper.OrdersOrderDetailMapper">
    <resultMap id="ordersUserOrderDetailMap" type="com.steven.bo.OrdersOrderDetail">
        <id column="order_id" property="orderId"/>
        <result column="order_no" property="orderNo"/>
        <result column="note" property="note"/>
        <collection ofType="com.steven.po.OrderDetail" property="orderDetailList">
            <id column="order_detail_id" property="orderDetailId"/>
            <result column="orderDetail_id" property="orderDetailId"/>
            <result column="order_id" property="orderId"/>
            <result column="item_id" property="itemId"/>
            <result column="item_num" property="itemNum"/>
        </collection>
    </resultMap>

    <select id="getOrdersOrderDetail" resultMap="ordersUserOrderDetailMap">
	    select a.*,b.username,b.address,c.item_id,c.item_num
	    from orders as a inner join user as b on a.user_id = b.id
	    inner join orderDetail as c on a.order_id = c.order_id
	</select>
</mapper>

(5).编写测试类
Test类中调整获取Mapper和业务操作代码，具体代码如下。

public class Test {
    public static void main(String[] args) throws Exception {
        //1.获取MyBatis全局配置文件流
        String resource = "config/mybatis.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        //2.根据MyBatis配置信息创建会话工厂
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //3.获取会话对象
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //4.获取Mapper
        OrdersOrderDetailMapper ordersOrderDetailMapper = sqlSession.getMapper(OrdersOrderDetailMapper.class);
        //5.业务操作
        List<OrdersOrderDetail> ordersOrderDetailList = ordersOrderDetailMapper.getOrdersOrderDetail();
        Iterator<OrdersOrderDetail> oodIterator = ordersOrderDetailList.iterator();
        while (oodIterator.hasNext()) {
            OrdersOrderDetail ordersOrderDetail = oodIterator.next();
            System.out.println("orderNo:" + ordersOrderDetail.getOrderNo());
            System.out.println("note:" + ordersOrderDetail.getNote());
            List<OrderDetail> orderDetailList = ordersOrderDetail.getOrderDetailList();
            System.out.println("orderDetailList:" + orderDetailList.size()+"条");
            Iterator<OrderDetail> odIterator = orderDetailList.iterator();
            while (odIterator.hasNext()) {
                OrderDetail orderDetail = odIterator.next();
                System.out.print("orderId:" + orderDetail.getOrderId());
                System.out.print(",itemId:" + orderDetail.getItemId());
                System.out.println(",itemNum:" + orderDetail.getItemNum());
            }
            System.out.println();
        }
        sqlSession.close();
    }
}

orderNo:20221207173000000001
note:Steven买了一台电脑和两部手机
orderDetailList:2条
orderId:1,itemId:1,itemNum:1
orderId:1,itemId:2,itemNum:2

orderNo:20221207173500000002
note:Sherry买了一部手机和两台电脑
orderDetailList:2条
orderId:2,itemId:1,itemNum:2
orderId:2,itemId:2,itemNum:1