Question

我有一个hybrid_property，它根据一对多关系的一些计算返回一个字符串。

hybrid_property表达式的原始sql是：这是原始的sql：

SELECT
  CASE
    WHEN s.quantity_received = 0 THEN "unreceived"
    WHEN s.dif = 0.0  THEN "received"
    WHEN s.dif > 0.0  THEN "partially_received"
    WHEN s.dif < 0.0  THEN "over_received"
  END as status
FROM (
      SELECT li.quantity_received, sum(li.quantity - li.received) as 'dif'
      FROM line_items as li
      WHERE li.o_id = xxx
) as s

模特

class LineItem(BaseModel):

    __table__ = Table('line_items', autoload=True)

   order = relationship("Order", backreef="line_itms", primaryjoin="Order.id == foregin(LineItem.o_id)")


class Order(BaseModel):

    __table__ = Table('orders', autoload=True)

    @hybrid_property
    def status(self):
        qty_received, qty_ordered = 0, 0

        for li in self.line_items:
            if li.status != "cancelled":
                qty_ordered += li.quantity
                qty_received += li.quantity_received

        if qty_received == 0:
            status = "unreceived"

        elif qty_received == qty_ordered:
            status = "received"

        elif qty_received < qty_ordered:
            status = "partially_received"

        elif qty_received > qty_ordered:
            status = "over_received"

        return status


    @status.expression
    def status(cls):
        line_items_calc = select([LineItem.quantity_received,
                    func.sum(LineItem.quantity - LineItem.quantity_received).label('dif')]) \
            .where(and_(LineItem.o_id == Order.id,
                   or_(LineItem.fulfillment_status != "cancelled",
                       LineItem.fulfillment_status == None))) \
            .alias()

        qq = select([
            case([
                 (qs.c.quantity_received == 0, "unreceived"),
                 (qs.c.dif == 0, "received"),
                 (qs.c.dif > 0, "partially_received"),
                 (qs.c.dif < 0, "over_received")]
             )]) \
             .select_from(line_items_calc) \
             .as_scalar()

        return qq

我有2个订单，o1和o2包含订单项：

  LineItem(o_id=o1.id, quantity=1, quantity_received=1)
  LineItem(o_id=o2.id, quantity=1, quantity_received=0)
  LineItem(o_id=o2.id, quantity=2, quantity_received=1)

订单1应具有状态＆＃34;已收到＆＃34;而Order2应该有＆＃34; partial_received＆＃34;。

但当我查询＆＃34;收到＆＃34;我什么都没得到，在查询＆＃34; partial_received＆＃34;我得到2个结果而不是一个。

看起来它没有通过Order.id过滤LineItems，所以它使用all来计算状态（因为total_qty将是4，而接收的总数将是2，这将给出＆＃34; partial_received＆＃34;）

Order.query().filter(Order.status == 'received').all()  # returns []
Order.query().filter(Order.status == 'partially_received').all()  # returns [Order1, Order2]

如果将.correlate_except(LineItem)添加到 line_items_calc 查询，我会收到以下错误：

OperationalError：（_ mysql_exceptions.OperationalError）（1054，＆＃34;未知列＆＃39; orders.id＆＃39;在＆＃39; where子句＆＃39;＆＃34;）[SQL：你＆＃39; SELECT count（*）AS count_1 \ nFROM（SELECT * \ nFROM命令\ nWHERE orders.account_id =％s AND（SELECT CASE WHEN（a_3.quantity_received = ％s）THEN％s WHEN（a_3.dif =％s）THEN％s WHEN（a_3.dif＆gt;％s）THEN％s WHEN（a_3.dif＆lt;％s）THEN％s END as a_2 \ nFROM（SELECT line_items.quantity_received AS quantity_received， sum（line_items.quantity - line_items.quantity_received）AS dif \ nFROM line_items \ nWHERE line_items.o_id = orders.id AND （line_items.fulfillment_status！=％s OR line_items.fulfillment_status IS NULL））AS a_3）=％s）AS a_1＆＃39;] [参数：（1L，0，＆＃39;未接收＆＃39;，0，＆＃39;收到＆＃39;，0，＆＃39;部分接收＆＃39;，0，＆＃39; over_received＆＃39;，＆＃39;取消＆＃39;， U＆＃39; over_received＆＃39）]

Answer 1

似乎你试图将表达式与最外层的查询相关联，但事实证明当前嵌套的子查询方法在MySQL中是不可行的，因为它does not allow correlated subqueries in FROM clause根本没有 - 与其他一些相比数据库只是不允许与以前的FROM列表项相关联，除非使用LATERAL。

另一方面，嵌套子查询是多余的，因为您可以在SELECT列表中的CASE表达式中使用聚合，但在当前子查询中混合使用非聚合和聚合表达式：

SELECT li.quantity_received, sum(li.quantity - li.received) as 'dif'

这很可能不是你想要的。其他一些数据库甚至不允许这样的查询执行，但如果ONLY_FULL_GROUP_BY被禁用，MySQL会默默地从组中未指定的行中选择li.quantity_received的值。默认情况下，它在5.7.5及更高版本中启用，您应该考虑启用它。看看你的混合财产的另一半看起来你可能也想收取收到数量的总和。

以下是状态表达式的一个版本，它满足您在问题中提出的2个测试用例：

 @status.expression
 def status(cls):
     qty_received = func.coalesce(func.sum(LineItem.quantity_received), 0)
     qty_ordered = func.coalesce(func.sum(LineItem.quantity), 0)

     return select([case([
             (qty_received == 0, "unreceived"),
             (qty_received == qty_ordered, "received"),
             (qty_received < qty_ordered, "partially_received"),
             (qty_received > qty_ordered, "over_received")])]).\
         where(and_(func.coalesce(LineItem.fulfillment_status, "") != "cancelled",
                    LineItem.o_id == cls.id)).\
         correlate_except(LineItem).\
         as_scalar()

我相信它比你原来更接近Python方法。请注意使用COALESCE进行NULL处理。

SQLAlchemy从case表达式引用子查询

1 个答案: