Raise exception instead of cause TypeError when polymorphic_ctype_id is invalid.

polymorphic/tests/models.py

@@ -218,7 +218,7 @@ class ChildModelWithManager(PolymorphicModel):
 class PlainMyManagerQuerySet(QuerySet):
 
     def my_queryset_foo(self):
-        return self.all()  # Just a method to prove the existance of the custom queryset.
+        return self.all()  # Just a method to prove the existence of the custom queryset.
 
 
 class PlainMyManager(models.Manager):

polymorphic/tests/test_orm.py

@@ -4,12 +4,12 @@ import uuid
 from django.contrib.contenttypes.models import ContentType
 from django.db import models
 from django.db.models import Case, Count, Q, When
-from django.test import TestCase, TransactionTestCase
+from django.test import TransactionTestCase
 from django.utils import six
 
 from polymorphic import query_translate
 from polymorphic.managers import PolymorphicManager
-from polymorphic.models import PolymorphicTypeUndefined
+from polymorphic.models import PolymorphicTypeInvalid, PolymorphicTypeUndefined
 from polymorphic.tests.models import (
     ArtProject,
     Base,
@@ -68,7 +68,6 @@ from polymorphic.tests.models import (
     ProxyModelA,
     ProxyModelB,
     ProxyModelBase,
-    QuerySet,
     RedheadDuck,
     RelationA,
     RelationB,
@@ -967,6 +966,17 @@ class PolymorphicTests(TransactionTestCase):
         with self.assertRaises(PolymorphicTypeUndefined):
             list(Model2A.objects.all())
 
+    def test_invalid_polymorphic_id(self):
+        """Test that a proper error message is displayed when the database lacks the ``polymorphic_ctype_id``"""
+        Model2A.objects.create(field1='A1')
+        Model2B.objects.create(field1='A1', field2='B2')
+        Model2B.objects.create(field1='A1', field2='B2')
+        invalid = ContentType.objects.get_for_model(PlainA).pk
+        Model2A.objects.all().update(polymorphic_ctype_id=invalid)
+
+        with self.assertRaises(PolymorphicTypeInvalid):
+            list(Model2A.objects.all())
+
     def test_bulk_create_abstract_inheritance(self):
         ArtProject.objects.bulk_create([
             ArtProject(topic='Painting with Tim', artist='T. Turner'),