Hi,
When using a OneToOneField? to make one model extend another, I noticed a behavioral inconsistency depending on whether the related model's OneToOneField? was also the primary key or not.
The inconsistency is to do with when save() can be called on model instances.
Consider the following example models:
class BaseModel(models.Model):
pass
class ExtendedModel(models.Model):
link = models.OneToOneField(BaseModel)
It is not possible to first instantiate these models and later on save them - an IntegrityError would be raised when saving the ExtendedModel?. E.g.,
o1 = BaseModel()
o2 = ExtendedModel(link=o1)
o1.save()
o2.save()
when o2 is saved it will raise an IntegrityError because it doesn't have a value for the primary key of the model it is related to. I think o1's primary key is copied when o2 is initialized, and is None at this point because o1 isn't saved yet.
However, if the definition of ExtendedModel? is changed so that the OneToOneField? is also the primary key, it now becomes possible to save the model instances in this order. To test this I changed the model definition as follows:
class ExtendedModel(models.Model):
link = models.OneToOneField(BaseModel, primary_key=True)
When using this model definition it seems that o1's primary key is copied when o2 is saved, as opposed to when o2 is initialized. This inconsistency caused a lot of head scratching here.
Thanks!
Sean
