Fix reverse relation support for ___ filter operator

docs/changelog.rst

@@ -1,6 +1,13 @@
 Changelog
 ==========
 
+Version 0.8.1 (2015-12-29)
+--------------------------
+
+* Fixed support for reverse relations for ``relname___field`` when the field starts with an ``_`` character.
+  Otherwise, the query will be interpreted as subclass lookup (``ClassName___field``).
+
+
 Version 0.8 (2015-12-28)
 ------------------------
 

polymorphic/query_translate.py

@@ -4,11 +4,25 @@
 """
 from __future__ import absolute_import
 
+import django
 from django.db import models
 from django.contrib.contenttypes.models import ContentType
 from django.db.models import Q, FieldDoesNotExist
 
-from django.db.models.fields.related import RelatedField  # Django 1.8
+from django.db.models.fields.related import RelatedField
+if django.VERSION < (1, 6):
+    # There was no common base class in Django 1.5, mention all variants here.
+    from django.db.models.fields.related import RelatedObject, ManyToOneRel, ManyToManyRel
+    REL_FIELD_CLASSES = (RelatedField, RelatedObject, ManyToOneRel, ManyToManyRel)  # Leaving GenericRel out.
+elif django.VERSION < (1, 8):
+    # As of Django 1.6 there is a ForeignObjectRel.
+    from django.db.models.fields.related import ForeignObjectRel, RelatedObject
+    REL_FIELD_CLASSES = (RelatedField, ForeignObjectRel, RelatedObject)
+else:
+    # As of Django 1.8 the base class serves everything. RelatedObject is gone.
+    from django.db.models.fields.related import ForeignObjectRel
+    REL_FIELD_CLASSES = (RelatedField, ForeignObjectRel)
+
 
 from functools import reduce
 
@@ -154,9 +168,13 @@ def translate_polymorphic_field_path(queryset_model, field_path):
         # Test whether it's actually a regular relation__ _fieldname (the field starting with an _)
         # so no tripple ClassName___field was intended.
         try:
-            # rel = (field_object, model, direct, m2m)
+            if django.VERSION >= (1, 8):
+                # This also retreives M2M relations now (including reverse foreign key relations)
                 field = queryset_model._meta.get_field(classname)
-            if isinstance(field, RelatedField):
+            else:
+                field = queryset_model._meta.get_field_by_name(classname)[0]
+
+            if isinstance(field, REL_FIELD_CLASSES):
                 # Can also test whether the field exists in the related object to avoid ambiguity between
                 # class names and field names, but that never happens when your class names are in CamelCase.
                 return field_path  # No exception raised, field does exist.

polymorphic/tests.py

@@ -159,7 +159,8 @@ class ModelUnderRelParent(PolymorphicModel):
 
 
 class ModelUnderRelChild(PolymorphicModel):
-    parent = models.ForeignKey(ModelUnderRelParent)
+    parent = models.ForeignKey(ModelUnderRelParent, related_name='children')
+    _private2 = models.CharField(max_length=10)
 
 
 class MyManagerQuerySet(PolymorphicQuerySet):
@@ -734,12 +735,20 @@ class PolymorphicTests(TestCase):
 
     def test_polymorphic___filter_field(self):
         p = ModelUnderRelParent.objects.create(_private=True, field1='AA')
-        ModelUnderRelChild.objects.create(parent=p)
+        ModelUnderRelChild.objects.create(parent=p, _private2=True)
 
         # The "___" filter should also parse to "parent" -> "_private" as fallback.
         objects = ModelUnderRelChild.objects.filter(parent___private=True)
         self.assertEqual(len(objects), 1)
 
+    def test_polymorphic___filter_reverse_field(self):
+        p = ModelUnderRelParent.objects.create(_private=True, field1='BB')
+        ModelUnderRelChild.objects.create(parent=p, _private2=True)
+
+        # Also test for reverse relations
+        objects = ModelUnderRelParent.objects.filter(children___private2=True)
+        self.assertEqual(len(objects), 1)
+
     def test_delete(self):
         self.create_model2abcd()