From cf2c97b620b6190341c712ea96e82a66009326be Mon Sep 17 00:00:00 2001
From: Carl Meyer <carl@oddbird.net>
Date: Fri, 1 Feb 2013 22:53:11 -0700
Subject: [PATCH] Avoid overriding prior calls to select_related in
 select_subclasses.

---
 CHANGES.rst                |  4 ++++
 model_utils/managers.py    |  4 ++++
 model_utils/tests/tests.py | 11 +++++++++++
 3 files changed, 19 insertions(+)

diff --git a/CHANGES.rst b/CHANGES.rst
index 6bff04b..3c0feaa 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -4,6 +4,10 @@ CHANGES
 tip (unreleased)
 ----------------
 
+- Add workaround for https://code.djangoproject.com/ticket/16855 in
+  InheritanceQuerySet to avoid overriding prior calls to
+  ``select_related()``. Thanks ivirabyan.
+
 - Added support for arbitrary levels of model inheritance in
   InheritanceManager. Thanks ivirabyan. (This feature only works in Django
   1.6+ due to https://code.djangoproject.com/ticket/16572).
diff --git a/model_utils/managers.py b/model_utils/managers.py
index 63bed83..6005bf7 100644
--- a/model_utils/managers.py
+++ b/model_utils/managers.py
@@ -20,7 +20,11 @@ class InheritanceQuerySet(QuerySet):
             if django.VERSION < (1, 6, 0):
                 levels = 1
             subclasses = self._get_subclasses_recurse(self.model, levels=levels)
+        # workaround https://code.djangoproject.com/ticket/16855
+        field_dict = self.query.select_related
         new_qs = self.select_related(*subclasses)
+        if isinstance(new_qs.query.select_related, dict) and isinstance(field_dict, dict):
+            new_qs.query.select_related.update(field_dict)
         new_qs.subclasses = subclasses
         return new_qs
 
diff --git a/model_utils/tests/tests.py b/model_utils/tests/tests.py
index c49bdf0..4d524cd 100644
--- a/model_utils/tests/tests.py
+++ b/model_utils/tests/tests.py
@@ -344,6 +344,17 @@ class InheritanceManagerTests(TestCase):
             self.child1)
 
 
+    def test_prior_select_related(self):
+        # Django 1.2 doesn't have assertNumQueries
+        if django.VERSION >= (1, 3):
+            with self.assertNumQueries(1):
+                obj = self.get_manager().select_related(
+                    "inheritancemanagertestchild1").select_subclasses(
+                    "inheritancemanagertestchild2").get(pk=self.child1.pk)
+                obj.inheritancemanagertestchild1
+
+
+
 class InheritanceManagerRelatedTests(InheritanceManagerTests):
     def setUp(self):
         self.related = InheritanceManagerTestRelated.objects.create()