<select id="getOrderItemByOrderNoAndUserId" resultMap="BaseResultMap" parameterType="map">
select <include refid="Base_Column_List"/>
from mall_order_item
where user_id = #{userId} and order_no = #{orderNo}
</select>
List<OrderItem> orderItemList = this.orderItemMapper.getOrderItemByOrderNoAndUserId(orderNo, userId);
因为orderNo是唯一的,这样获取的就是唯一的OrderItem对象,为什么要用orderItemList集合去接收查询到的结果呢?