Fixed #22207 -- Added support for GenericRelation reverse lookups

GenericRelation now supports an optional related_query_name argument.
Setting related_query_name adds a relation from the related object back to
the content type for filtering, ordering and other query operations.

Thanks to Loic Bistuer for spotting a couple of important issues in
his review.

4 files changed, 23 insertions, 5 deletions

diff --git a/tests/generic_relations/models.py b/tests/generic_relations/models.py
index 436f26afb6..5d24e017a2 100644
--- a/tests/generic_relations/models.py
+++ b/tests/generic_relations/models.py
@@ -68,7 +68,7 @@ class Animal(models.Model):
     common_name = models.CharField(max_length=150)
     latin_name = models.CharField(max_length=150)
 
-    tags = GenericRelation(TaggedItem)
+    tags = GenericRelation(TaggedItem, related_query_name='animal')
     comparisons = GenericRelation(Comparison,
                                   object_id_field="object_id1",
                                   content_type_field="content_type1")
@@ -116,7 +116,7 @@ class Rock(Mineral):
 
 class ManualPK(models.Model):
     id = models.IntegerField(primary_key=True)
-    tags = GenericRelation(TaggedItem)
+    tags = GenericRelation(TaggedItem, related_query_name='manualpk')
 
 
 class ForProxyModelModel(models.Model):
diff --git a/tests/generic_relations/tests.py b/tests/generic_relations/tests.py
index ed12c5e92b..ae90ace34a 100644
--- a/tests/generic_relations/tests.py
+++ b/tests/generic_relations/tests.py
@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 from django import forms
 from django.contrib.contenttypes.forms import generic_inlineformset_factory
 from django.contrib.contenttypes.models import ContentType
+from django.core.exceptions import FieldError
 from django.test import TestCase
 from django.utils import six
 
@@ -42,6 +43,17 @@ class GenericRelationsTests(TestCase):
         # You can easily access the content object like a foreign key.
         t = TaggedItem.objects.get(tag="salty")
         self.assertEqual(t.content_object, bacon)
+        qs = TaggedItem.objects.filter(animal__isnull=False).order_by('animal__common_name', 'tag')
+        self.assertQuerysetEqual(
+            qs, ["<TaggedItem: hairy>", "<TaggedItem: yellow>", "<TaggedItem: fatty>"]
+        )
+        mpk = ManualPK.objects.create(id=1)
+        mpk.tags.create(tag='mpk')
+        from django.db.models import Q
+        qs = TaggedItem.objects.filter(Q(animal__isnull=False) | Q(manualpk__id=1)).order_by('tag')
+        self.assertQuerysetEqual(
+            qs, ["fatty", "hairy", "mpk", "yellow"], lambda x: x.tag)
+        mpk.delete()
 
         # Recall that the Mineral class doesn't have an explicit GenericRelation
         # defined. That's OK, because you can create TaggedItems explicitly.
@@ -151,6 +163,12 @@ class GenericRelationsTests(TestCase):
             "<Animal: Platypus>"
         ])
 
+    def test_generic_relation_related_name_default(self):
+        # Test that GenericRelation by default isn't usable from
+        # the reverse side.
+        with self.assertRaises(FieldError):
+            TaggedItem.objects.filter(vegetable__isnull=True)
+
     def test_multiple_gfk(self):
         # Simple tests for multiple GenericForeignKeys
         # only uses one model, since the above tests should be sufficient.
diff --git a/tests/generic_relations_regress/tests.py b/tests/generic_relations_regress/tests.py
index eaa8a743bd..481101f83f 100644
--- a/tests/generic_relations_regress/tests.py
+++ b/tests/generic_relations_regress/tests.py
@@ -245,5 +245,5 @@ class GenericRelationTests(TestCase):
         form = GenericRelationForm({'links': None})
         self.assertTrue(form.is_valid())
         form.save()
-        links = HasLinkThing._meta.get_field_by_name('links')[0].field
+        links = HasLinkThing._meta.get_field_by_name('links')[0]
         self.assertEqual(links.save_form_data_calls, 1)
diff --git a/tests/prefetch_related/models.py b/tests/prefetch_related/models.py
index 7d300ea84c..8fec5d4b7b 100644
--- a/tests/prefetch_related/models.py
+++ b/tests/prefetch_related/models.py
@@ -145,11 +145,11 @@ class TaggedItem(models.Model):
 
 class Bookmark(models.Model):
     url = models.URLField()
-    tags = GenericRelation(TaggedItem, related_name='bookmarks')
+    tags = GenericRelation(TaggedItem, related_query_name='bookmarks')
     favorite_tags = GenericRelation(TaggedItem,
                                     content_type_field='favorite_ct',
                                     object_id_field='favorite_fkey',
-                                    related_name='favorite_bookmarks')
+                                    related_query_name='favorite_bookmarks')
 
     class Meta:
         ordering = ['id']