App Engine NDB Datastore Property Subclasses - Float OR Integer

Question

I am trying to create an NDB property subclass that allows me to store a Number as either an ndb.IntegerProperty (if the Number is an int) or as an ndb.FloatProperty (if the Number is a float).

class Integer(ndb.Model):
    number = ndb.IntegerProperty()

class Real(ndb.Model):
    number = ndb.FloatProperty()


class NumberProperty(ndb.StructuredProperty):
    def _validate(self, value):
        assert isinstance(value, (int, float))

    def _to_base_type(self, value):
        if isinstance(value, int):
            return Integer(number=value)
        else:
            return Real(number=value)

    def _from_base_type(self, value):
        return value.number

Then I create a test class that uses this NumberProperty and try to create an entity:

class MyNumber(ndb.Model):
    value = NumberProperty()

MyNumber(value=12)

I receive the following TypeError: init() takes at least 2 arguments (1 given).

Please give me a hint how I should set up the required subclass. I tried many other forms, but nothing that works. Thanks.

Answer 1

Eventually I found that the following works best:

class NumberProperty(ndb.GenericProperty):
    def _validate(self, value):
        assert isinstance(value, (int, long, float))
        return value

Answer 2

Try something like this:

class NumberModel(ndb.Model):
    i = ndb.IntegerProperty()
    f = ndb.FloatProperty()

class NumberProperty(ndb.StructuredProperty):
    def _validate(self, value):
        assert isinstance(value, (int, float))

    def _to_base_type(self, value):
        if isinstance(value, int):
            return NumberModel(i=value)
        else:
            return NumberModel(f=value)

    def _from_base_type(self, value):
        v = value.i if value.i is not None else value.f
        return v

https://developers.google.com/appengine/docs/python/ndb/subclassprop