DRF - Getting 'NoneType object is not callable' error on delete instance from ModelViewSet - postgresql

Question

I am getting TypeError, when I try to delete Warehouse instance.
Note: If I delete Shop instance, Warehouse under that Shop needs be deleted, that's why I used on_delete=models.CASCADE.
class Warehouse(models.Model):
"""Warehouse model"""
name = models.CharField(max_length=255)
shop = models.ForeignKey(Shop, on_delete=models.CASCADE)
class WarehouseViewSet(viewsets.ModelViewSet):
"""Viewset"""
queryset = models.Warehouse.objects.all()
serializer_class = serializers.WarehouseSerializer
Error:
TypeError: 'NoneType' object is not callable
[14/Feb/2021 22:10:46] "DELETE /api/v1/shop/warehouse/2/ HTTP/1.1" 500 113266
Internal Server Error: /api/v1/shop/warehouse/2/
Traceback (most recent call last):
File "C:\Python38\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
response = get_response(request)
File "C:\Python38\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
response = self.process_exception_by_middleware(e, request)
File "C:\Python38\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\Python38\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "C:\Python38\lib\site-packages\rest_framework\viewsets.py", line 114, in view
return self.dispatch(request, *args, **kwargs)
File "C:\Python38\lib\site-packages\rest_framework\views.py", line 505, in dispatch
response = self.handle_exception(exc)
File "C:\Python38\lib\site-packages\rest_framework\views.py", line 465, in handle_exception
self.raise_uncaught_exception(exc)
File "C:\Python38\lib\site-packages\rest_framework\views.py", line 476, in raise_uncaught_exception
raise exc
File "C:\Python38\lib\site-packages\rest_framework\views.py", line 502, in dispatch
response = handler(request, *args, **kwargs)
File "C:\Python38\lib\site-packages\rest_framework\mixins.py", line 91, in destroy
self.perform_destroy(instance)
File "C:\Python38\lib\site-packages\rest_framework\mixins.py", line 95, in perform_destroy
instance.delete()
File "C:\Python38\lib\site-packages\django\db\models\base.py", line 921, in delete
collector.collect([self], keep_parents=keep_parents)
File "C:\Python38\lib\site-packages\django\db\models\deletion.py", line 224, in collect
field.remote_field.on_delete(self, field, sub_objs, self.using)

Answer 1

Found the solution. I did not handle on_delete for Children model.
SOLUTION
class WarehouseChildren(models.Model):
data = models.PositiveIntegerField(default=0)
warehouse = models.ForeignKey(Warehouse, on_delete=models.SET_NULL, null=True)
or
class WarehouseChildren(models.Model):
data = models.PositiveIntegerField(default=0)
warehouse = models.ForeignKey(Warehouse, on_delete=models.CASCADE)