mybatis0205 一对多查询 复杂

1.1sql
主查询表：用户信息
关联查询：订单、订单明细，商品信息

SELECT 
  orders.*,
  user.username,
  user.sex ,
  orderdetail.id orderdetail_id,
  orderdetail.items_num,
  orderdetail.items_id,
  items.name items_name,
  items.detail items_detail
FROM
  orders,
  USER,
  orderdetail,
  items
WHERE orders.user_id = user.id  AND orders.id = orderdetail.orders_id AND items.id = orderdetail.items_id

pojo定义

在user.java(主表)中创建映射的属性：集合 List<Orders>  orderlist
在Orders中创建映射的属性：集合List<Orderdetail> orderdetails 
在Orderdetail中创建商品属性：pojo   Items items

<!-- 一对多查询使用reusltMap完成
    查询用户及订单和订单明细，关联商品，的信息
     -->
     <select id="findUserOrderDetail" resultMap="userOrderDetailResultMap" >
    SELECT 
  orders.*,
  user.username,
  user.sex ,
  orderdetail.id orderdetail_id,
  orderdetail.items_num,
  orderdetail.items_id,
  items.name items_name,
  items.detail items_detail
FROM
  orders,
  USER,
  orderdetail,
  items
WHERE orders.user_id = user.id  AND orders.id = orderdetail.orders_id AND items.id = orderdetail.items_id
     </select>

将查询的数据库结果和User接收对象进行映射
<!-- 一对多查询，查询用户及订单明细和商品信息 -->
    <resultMap type="user" id="userOrderDetailResultMap">
        <!-- 用户信息User映射 -->
        <id column="user_id" property="id"/>id是User的属性，user_id是查询的数据库表的列名
        <result column="username" property="username"/>
        <result column="sex" property="sex"/>
        <!-- 订单信息，orderlist是User的属性 -->
        <collection property="orderlist" ofType="cn.itcast.mybatis.po.Orders">
                <id column="id" property="id"/>id是Orders的属性，id是查询的数据库表的列名
                <result column="user_id" property="userId"/>
                <result column="number" property="number"/>
                <result column="createtime" property="createtime"/>
                <result column="note" property="note"/>
                <!-- 订单明细映射 -->
                <collection property="orderdetails" ofType="cn.itcast.mybatis.po.Orderdetail">
                    <!-- id：关联信息订单明细的唯 一标识
                    property：Orderdetail的属性名
                      -->
                    <id column="orderdetail_id" property="id"/>
                    <result column="items_num" property="itemsNum"/>
                    <result column="items_id" property="itemsId"/>
                    <!-- 商品信息 -->
                    <association property="items" javaType="cn.itcast.mybatis.po.Items">
                        <id column="item_id" property="id"/>
                        <result column="items_name" property="name"/>
                        <result column="items_detail" property="detail"/>
                    </association>
                </collection>
        </collection>

        
    
    </resultMap>

// 一对多查询使用resultMap
    @Test
    public void testFindUserOrderDetail() throws Exception {

        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 创建mapper代理对象
        OrdersMapperCustom ordersMapperCustom = sqlSession
                .getMapper(OrdersMapperCustom.class);

        // 调用方法
        List<User> list = ordersMapperCustom.findUserOrderDetail();

        System.out.println(list);
    }