Support ForeignKey based model inheritance

[James Pic]

Currently, a model inheriting another will have a 1:1 relation with an automatically managed OneToOneField. This means a parent model instance may only have one child model instance. However, sometimes it may be interresting to have several child model instances for one parent model instance.

For example, creating a new child model with the same parent results in an error like:

django.db.utils.IntegrityError: UNIQUE constraint failed: djcall_call.callable_ptr_id

But overriding the parent field with a ForeignKey is not accepted:

django.core.exceptions.FieldError: Auto-generated field 'callable_ptr' in class 'Call' for parent_link to base class 'Callable' clashes with declared field of the same name.

Can we perhaps add an exception (not Exception!) for child models that override the automatic ptr field that is a OneToOneField, with a ForeignKey ?

An example use case:

class Caller(models.Model):
    callback = models.CharField()
    max_attemps = models.IntegerField(default=1)

    def call(self):
         call = Call(caller_ptr=self)
         try:
             call.execute()
         except:
             if self.max_attempts > Call.objects.filter(caller_ptr=self):
                 return self.call()
             raise
         return call.result

class Call(Caller):
    result = models.PickleField()

    def call(self):
         self.result = import_string(self.callback)()
         return self.result

Thanks