Fixed applabel__ModelName___field looksups

Closes: #286
(cherry picked from commit 8f0932b71e)

polymorphic/query_translate.py

@@ -7,6 +7,8 @@ from __future__ import absolute_import
 import copy
 import django
 from functools import reduce
+
+from django.apps import apps
 from django.contrib.contenttypes.models import ContentType
 from django.db import models
 from django.db.models.fields.related import ForeignObjectRel, RelatedField
@@ -148,7 +150,7 @@ def translate_polymorphic_field_path(queryset_model, field_path):
     if '__' in classname:
         # the user has app label prepended to class name via __ => use Django's get_model function
         appname, sep, classname = classname.partition('__')
-        model = models.get_model(appname, classname)
+        model = apps.get_model(appname, classname)
         assert model, 'PolymorphicModel: model %s (in app %s) not found!' % (model.__name__, appname)
         if not issubclass(model, queryset_model):
             e = 'PolymorphicModel: queryset filter error: "' + model.__name__ + '" is not derived from "' + queryset_model.__name__ + '"'

polymorphic/tests/test_orm.py

@@ -427,6 +427,18 @@ class PolymorphicTests(TestCase):
         self.assertEqual(repr(objects[0]), '<Model2B: id 2, field1 (CharField), field2 (CharField)>')
         self.assertEqual(repr(objects[1]), '<Model2C: id 3, field1 (CharField), field2 (CharField), field3 (CharField)>')
 
+    def test_polymorphic_applabel___filter(self):
+        self.create_model2abcd()
+
+        self.assertEqual(Model2B._meta.app_label, 'polymorphic')
+        objects = Model2A.objects.filter(Q(polymorphic__Model2B___field2='B2') | Q(polymorphic__Model2C___field3='C3'))
+        self.assertQuerysetEqual(
+            objects,
+            [Model2B, Model2C],
+            transform=lambda o: o.__class__,
+            ordered=False,
+        )
+
     def test_query_filter_exclude_is_immutable(self):
         # given
         q_to_reuse = Q(Model2B___field2='something')