使用模型继承时 ndb.KeyProperty 可以引用基模型类吗? [英] Can ndb.KeyProperty reference a base model class when using model inheritance?

问题描述

我有一些共享一组通用属性的模型，我在其他模型继承的基础模型类中定义了这些属性:

I have some models that share a common set of properties, which I have defined in a base model class from which other models inherit:

class BaseUser(ndb.Model):
    name = ndb.StringProperty()

class DerivedUserA(BaseUser):
    # some additional properties...

class DerivedUserB(BaseUser):
    # some additional properties...

在其他一些模型中，我需要对任何 BaseUser 派生模型的引用:

In some other model, I need a reference to any BaseUser-derived model:

class MainModel(ndb.Model):
    user = ndb.KeyProperty(kind = BaseUser)

但是，当我尝试将 DerivedUserA 实体键设置为 MainModel.user 属性时，GAE 会引发 BadValueError 说明它是期待一个类型为 BaseUser 的密钥，但得到了一个 DerivedUserA.

However, When I try to set a DerivedUserA entity key to the MainModel.user property, GAE raises a BadValueError stating that it is expecting a key with kind BaseUser but was given a DerivedUserA.

如果我从我的 MainModel 中删除 kind 参数，它会起作用:

If I remove the kind argument from my MainModel, it works:

class MainModel(ndb.Model):
    user = ndb.KeyProperty()

我可以接受，但我宁愿进行检查以确保我没有尝试在 MainModel.user 属性中保存任何类型的实体.有没有办法做到这一点?

I could live with that, but I'd rather have a check in place to make sure that I am not trying to save any kind of entity in the MainModel.user property. Is there a way to do that?

推荐答案

使用 PolyModel 进行数据存储继承 -> https://developers.google.com/appengine/docs/python/ndb/polymodelclass

Use PolyModel for datastore inheritance -> https://developers.google.com/appengine/docs/python/ndb/polymodelclass

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