MyBatis学习20-多对多查询

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1.需求：查询用户及用户购买的商品信息

  查询主表是：用户表

  关联表：由于用户和商品没有直接关联，通过订单和订单明细进行关联，所以关联表：orders、orderdetail、items

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

映射思路：

将用户信息映射到user中。

在user类中添加订单列表属性List<Orders> orderslist，将用户创建的订单映射到orderslist

在Orders中添加订单明细列表属性List<OrderDetail>orderdetials，将订单的明细映射到orderdetials

在OrderDetail中添加Items属性，将订单明细所对应的商品映射到Items

2.写mapper.xml

<resultMap type="po.User" id="UserAndItemsResultMap">
<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="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="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="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="findUserAndItemsResultMap" resultMap="UserAndItemsResultMap">
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>

3.写mapper.java

public List<User> findUserAndItemsResultMap() throws Exception;

4.写测试程序，测试成功

@Test
public void testFindUserAndItemsResultMap() throws Exception {

SqlSession sqlSession = sqlSessionFactory.openSession();
OrdersMapperCustom ordersMapperCustom = sqlSession
.getMapper(OrdersMapperCustom.class);

List<User> list = ordersMapperCustom.findUserAndItemsResultMap();

System.out.println(list);

sqlSession.close();
}

MyBatis学习20-多对多查询

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原文地址：http://www.cnblogs.com/hqt2050/p/4987343.html