Problematic is_new_object based on primary key with default uuid

[Kub-AT]

Hi.

There is a problem with Models which have primary key with default=uuid

id = models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True)

The initial/first field history value is not saved to database.
It is caused by is_new_object = instance.pk is None in tracker.py

This approach has a problem:
In the save method, self.pk will never be None when default=uuid.uuid is set.

A large number of django users (and a lot of non-official django tutorials) believe that checking self.pk in the save method is a safe way to detect and decide whether an instance of a model is new or not.

No its not. The safe way to detect and decide whether an instance of a model is new or not is to use self._state object
https://docs.djangoproject.com/en/3.2/ref/models/instances/#state

So I think you should switch from
is_new_object = instance.pk is None
to
is_new_object = instance._state.adding