easier way of detecting Multi-table inheritance

management/commands/_import_utils.py

@@ -7,8 +7,6 @@ from collections import defaultdict
 from django.apps import apps
 from django.db import transaction
 
-from django.contrib.auth.models import User
-from django.db.models import Model
 from polymorphic.models import PolymorphicModel
 
 
@@ -67,7 +65,9 @@ class BulkCreateManager(object):
 
     def _commit(self, model_class):
         model_key = model_class._meta.label
-        if model_class.__base__ in [Model, PolymorphicModel] or model_class is User:
+        # check for mutli-table inheritance it happens
+        # if model_class is a grand-child of PolymorphicModel
+        if model_class.__base__ is not PolymorphicModel and model_class.__base__.__base__ is PolymorphicModel:
             model_class.objects.bulk_create(self._create_queues[model_key])
         else:
             # ensure that parents models exists