CODEWITHSUNDEEP
pythongoogle-app-enginegoogle-cloud-datastoreapp-engine-ndb
ThePloki
ThePloki

Reputation: 185

GAE NDB Expando Model with dynamic Kind

Is it possible to assign a dynamic Entity Kind to an Expando Model? For example, I want to use this model for many types of dynamic entities:

class Dynamic(ndb.Expando):
    """
    Handles all "Post types", such as Pages, Posts, Users, Products, etc...
    """
    col = ndb.StringProperty()
    parent = ndb.IntegerProperty()
    name = ndb.StringProperty()
    slug = ndb.StringProperty()

Right now I use the "col" StringProperty to hold the Kind (like "Pages", "Posts", etc) and query for the "col" every time.

After reading the docs, I stumbled upon this @classmethod:

class MyModel(ndb.Model):
    @classmethod
    def _get_kind(cls):
         return 'AnotherKind'

Does that mean I can do this?

class Dynamic(ndb.Expando):
    """
    Handles all "Post types", such as Pages, Posts, Users, Products, etc...
    """
    col = ndb.StringProperty()
    parent = ndb.IntegerProperty()
    name = ndb.StringProperty()
    slug = ndb.StringProperty()

    @classmethod
    def _get_kind(cls):
        return 'AnotherKind'

But how do I dynamically replace 'AnotherKind'? Can I do something like return col?

Thanks!

Upvotes: 0

Views: 208

Answers (1)

minou
minou

Reputation: 16563

I don't know if you can do that, but it sounds dangerous, and GAE updates might break your code.

Using subclasses seems like a much safer alternative. Something like this:

class Dynamic(ndb.Expando):
    parent = ndb.IntegerProperty()
    name = ndb.StringProperty()
    slug = ndb.StringProperty()

class Pages(Dynamic):
    pass

class Posts(Dynamic):
    pass

class Users(Dynamic):
    pass

You could also try using PolyModel.

We need to know more about your application and what you are trying to accomplish to give more specific advice.

Upvotes: 1

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