Question

I want my model to get a GUID as key_name automatically and I’m using the code below. Is that a good approach to solve it? Does it have any drawbacks?

class SyncModel(polymodel.PolyModel):
    def __init__(self, key_name=None, key=None, **kwargs):
        super(SyncModel, self).__init__(key_name=str(uuid.uuid1()) if not key else None,key=key, **kwargs)

Answer 1

Overriding __init__ on a Model subclass is dangerous, because the constructor is used by the framework to reconstruct instances from the datastore, in addition to being used by user code. Unless you know exactly how the constructor is used to reconstruct existing entities – something which is an internal detail and may change in future – you should avoid overriding it.

Instead, define a factory method, like this:

class MyModel(db.Model):
  @classmethod
  def new(cls, **kwargs):
    return cls(key_name=str(uuid.uuid4()), **kwargs)