ndb.StructuredProperty不调用ndb.PolyModel子类方法 [英] ndb.StructuredProperty not calling ndb.PolyModel subclass methods

问题描述

在将ndb.Polymodel超类存储为ndb.StructuredProperty时，我无法访问子类方法;超类方法被调用，并引发NotImplementedError。

While storing ndb.Polymodel superclasses as an ndb.StructuredProperty, I was unable to access subclass methods; superclass methods were called instead and raising NotImplementedError's. Here is an abridged version of what I am trying to accomplish.

class Recipient(polymodel.PolyModel):
  name = ndb.StringProperty()

  def PrettyPrinting(self):
    raise NotImplementedError, 'Rawr'


class ShippingRecipient(Recipient):
  address_line_one = ndb.StringProperty()
  #there are other properties, but they aren't necessary here.

  def PrettyPrinting(self):
    return 'Hey, this should be called.'


class LocalRecipient(Recipient):
  distribution_location = ndb.StringProperty()
  #same deal, more attributes, but useless for this example.

  def PrettyPrinting(self):
    return 'Hey this should be called.'

class Shipment(ndb.Model):
  recipient = ndb.StructuredProperty(Recipient)

现在说我已经保存了一批货物并将ShippingRecipient存储到了货件的收件人领域。在数据存储中，货件recipient.class == ['Recipient'，'ShippingRecipient']。当我打电话时：

Now say that I have saved a shipment and stored a ShippingRecipient into the shipment's recipient field. In the datastore, the shipment recipient.class == ['Recipient', 'ShippingRecipient']. When I call:

shipment = Shipment.get_by_id('some_key')
shipment.recipient.PrettyPrinting()

引发NotImplementedError，而不是PrettyPrinting（...）的ShippingRecipient实现。我希望在访问货件的收件人字段时调用子类方法。有没有办法，我可以到达子类方法呢？我知道说结构化属性是Recipient类型会导致超类方法被调用，但是可能我不完全理解他们为什么要将子类存储在recipient.class属性中。

The NotImplementedError is raised instead of the ShippingRecipient implementation of PrettyPrinting(...). I want the subclass method to be called when accessing the shipment's recipient field. Is there a way I can get to the subclass method instead? I know that saying the structured property is of type Recipient causes the superclass method to be called, but then maybe I don't fully understand why they would store the subclass in the recipient.class attribute.

推荐答案

我不相信这可以工作。它只会存储Recipient实例。

如果你看看PolyModel是如何工作的，所有变体都存储为基类，
在你的示例 Recipient 。它还存储子类名称，当它从数据存储中检索时，它会重新创建特定的子类。

I don't believe this can work. It will only store Recipient instances.
If you look at how PolyModel works, all variants are stored as the base class, in your example Recipient. It also stores the sub class names, when and entity it is retrieved from the data store, it recreates the specific subclass.

我真的怀疑他们会将此机制构建到StructuredProperty实例化中，并且您已经发现这种情况。

I really doubt they would have built this mechanism into StructuredProperty instantiation, and you have found this to be the case.

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