  
  class ParkingLot3(Place):
      # The parent_link connector need not be the pk on the model.
      primary_key = models.AutoField(primary_key=True)
      parent = models.OneToOneField(Place, parent_link=True)
  
  
  class ParkingLot4(models.Model):
      # Test parent_link connector can be discovered in abstract classes.
      parent = models.OneToOneField(Place, parent_link=True)
 
</s> remove     parent = models.OneToOneField(Place, parent_link=True)
 </s> add     parent = models.OneToOneField(Place, models.CASCADE, parent_link=True) </s> remove     parent = models.OneToOneField(Place)
 </s> add     parent = models.OneToOneField(Place, models.CASCADE) </s> remove     parent = models.OneToOneField(Place, primary_key=True, parent_link=True)
 </s> add     parent = models.OneToOneField(Place, models.CASCADE, primary_key=True, parent_link=True) </s> remove     parent = models.OneToOneField(Place, primary_key=True, parent_link=True)
    main_site = models.ForeignKey(Place, related_name='lot')
 </s> add     parent = models.OneToOneField(Place, models.CASCADE, primary_key=True, parent_link=True)
    main_site = models.ForeignKey(Place, models.CASCADE, related_name='lot') </s> remove     media = models.OneToOneField(Media, primary_key=True, parent_link=True)
 </s> add     media = models.OneToOneField(Media, models.CASCADE, primary_key=True, parent_link=True)
    parent = models.OneToOneField(Place, models.CASCADE, parent_link=True)
  
  class ParkingLot3(Place):
      # The parent_link connector need not be the pk on the model.
      primary_key = models.AutoField(primary_key=True)
    parent = models.OneToOneField(Place, models.CASCADE, parent_link=True)
  
  
  class ParkingLot4(models.Model):
      # Test parent_link connector can be discovered in abstract classes.
      parent = models.OneToOneField(Place, parent_link=True)
keep keep keep keep replace keep keep keep keep keep
 Fixed #21127 -- Started deprecation toward requiring on_delete for ForeignKey/OneToOneField 
tests/model_inheritance_regress/models.py