一、应用场景
查询所有用户及其购买的商品
第一步
修改user，让其持有orders的集合list
第二步
修改orders让其持有orderdetail集合
第三步
修改orderdetail，让其持有item对象
Mapper.xml配置文件
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<resultMap type="com.james.po.User" id="selectUserAllItemResultMap">
<id column="user_id" property="id"/>
<result column="username" property="userName"/>
<result column="sex" property="sex"/>
<result column="address" property="address"/>
<collection property="ordersList" ofType="com.james.po.Orders">
<id column="id" property="id"/>
<result column="user_id" property="userId"/>
<result column="number" property="number"/>
<result column="createtime" property="createtime"/>
<result column="note" property="note"/>
<collection property="orderdetails" ofType="com.james.po.Orderdetail">
<id column="orderdetail_id" property="id"/>
<result column="items_id" property="itemsId"/>
<result column="items_num" property="itemsNum"/>
<result column="orders_id" property="ordersId"/>
<association property="items" javaType="com.james.po.Items">
<id column="items_id" property="id"/>
<result column="items_name" property="name"/>
<result column="items_detail" property="detail"/>
<result column="items_price" property="price"/>
</association>
</collection>
</collection>
</resultMap>
<select id="selectUserAllItem" resultMap="selectUserAllItemResultMap">
SELECT
orders.*,
USER.username,
USER.sex,
USER.address,
orderdetail.id orderdetail_id,
orderdetail.items_id,
orderdetail.items_num,
orderdetail.orders_id,
items.name items_name,
items.detail items_detail,
items.price items_price
FROM
orders,USER,orderdetail,items
WHERE orders.user_id = user.id AND orderdetail.orders_id=orders.id AND orderdetail.items_id = items.id
</select>
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