  
  class UUIDPKChildOfAutoPKParent(models.Model):
      uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
      name = models.CharField(max_length=255)
      parent = models.ForeignKey(AutoPKParent)
  
  
  class ParentWithUUIDAlternateKey(models.Model):
      uuid = models.UUIDField(unique=True, default=uuid.uuid4, editable=False)
      name = models.CharField(max_length=50)
 
</s> remove     parent = models.ForeignKey(UUIDPKParent)
 </s> add     parent = models.ForeignKey(UUIDPKParent, models.CASCADE) </s> remove     current_room = models.ForeignKey(Room, related_name='fleas', null=True)
 </s> add     current_room = models.ForeignKey(Room, models.SET_NULL, related_name='fleas', null=True) </s> remove     parent = models.ForeignKey(Parent, editable=False)
 </s> add     parent = models.ForeignKey(Parent, models.CASCADE, editable=False) </s> remove     parent = models.ForeignKey(UUIDPKParent)
 </s> add     parent = models.ForeignKey(UUIDPKParent, models.CASCADE) </s> remove     parent = models.ForeignKey(UUIDPKParent)
 </s> add     parent = models.ForeignKey(UUIDPKParent, models.CASCADE)
    parent = models.ForeignKey(AutoPKParent, models.CASCADE)
  
  class UUIDPKChildOfAutoPKParent(models.Model):
      uuid = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
      name = models.CharField(max_length=255)
    parent = models.ForeignKey(AutoPKParent, models.CASCADE)
  
  
  class ParentWithUUIDAlternateKey(models.Model):
      uuid = models.UUIDField(unique=True, default=uuid.uuid4, editable=False)
      name = models.CharField(max_length=50)
keep keep keep keep replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/model_formsets/models.py