[1.7.x] Fixed #23604 -- Allowed related m2m fields to be references in the admin.

Thanks Simon Charette for review.

Backport of a24cf217 from master

django/contrib/admin/options.py

@@ -447,6 +447,11 @@ class BaseModelAdmin(six.with_metaclass(RenameBaseModelAdminMethods)):
         except FieldDoesNotExist:
             return False
 
+        # Check whether this model is the origin of a M2M relationship
+        # in which case to_field has to be the pk on this model.
+        if opts.many_to_many and field.primary_key:
+            return True
+
         # Make sure at least one of the models registered for this site
         # references this field through a FK or a M2M relationship.
         registered_models = set()

docs/releases/1.4.16.txt

@@ -4,12 +4,15 @@ Django 1.4.16 release notes
 
 *Under development*
 
-Django 1.4.16 fixes a regression in the 1.4.14 security release and a bug
-preventing the use of some GEOS versions with GeoDjango.
+Django 1.4.16 fixes a couple regressions in the 1.4.14 security release and a
+bug preventing the use of some GEOS versions with GeoDjango.
 
 Bugfixes
 ========
 
+* Allowed related many-to-many fields to be referenced in the admin
+  (`#23604 <http://code.djangoproject.com/ticket/23604>`_).
+
 * Allowed inline and hidden references to admin fields
   (`#23431 <http://code.djangoproject.com/ticket/23431>`_).
 

docs/releases/1.5.11.txt

@@ -4,10 +4,13 @@ Django 1.5.11 release notes
 
 *Under development*
 
-Django 1.5.11 fixes a regression in the 1.5.9 security release.
+Django 1.5.11 fixes a couple regressions in the 1.5.9 security release.
 
 Bugfixes
 ========
 
+* Allowed related many-to-many fields to be referenced in the admin
+  (`#23604 <http://code.djangoproject.com/ticket/23604>`_).
+
 * Allowed inline and hidden references to admin fields
   (`#23431 <http://code.djangoproject.com/ticket/23431>`_).

docs/releases/1.6.8.txt

@@ -4,9 +4,12 @@ Django 1.6.8 release notes
 
 *Under development*
 
-Django 1.6.8 fixes a regression in the 1.6.6 security release.
+Django 1.6.8 fixes a couple regressions in the 1.6.6 security release.
 
 Bugfixes
 ========
 
+* Allowed related many-to-many fields to be referenced in the admin
+  (:ticket:`23604`).
+
 * Allowed inline and hidden references to admin fields (:ticket:`23431`).

docs/releases/1.7.1.txt

@@ -9,6 +9,9 @@ Django 1.7.1 fixes several bugs in 1.7.
 Bugfixes
 ========
 
+* Allowed related many-to-many fields to be referenced in the admin
+  (:ticket:`23604`).
+
 * Added a more helpful error message if you try to migrate an app without first
   creating the ``contenttypes`` table (:ticket:`22411`).
 

tests/admin_views/admin.py

@@ -37,7 +37,7 @@ from .models import (Article, Chapter, Child, Parent, Picture, Widget,
     State, City, Restaurant, Worker, ParentWithDependentChildren,
     DependentChild, StumpJoke, FieldOverridePost, FunkyTag,
     ReferencedByParent, ChildOfReferer, M2MReference, ReferencedByInline,
-    InlineReference, InlineReferer)
+    InlineReference, InlineReferer, Ingredient)
 
 
 def callable_year(dt_value):
@@ -932,6 +932,7 @@ site.register(EmptyModelHidden, EmptyModelHiddenAdmin)
 site.register(EmptyModelVisible, EmptyModelVisibleAdmin)
 site.register(EmptyModelMixin, EmptyModelMixinAdmin)
 site.register(StumpJoke)
+site.register(Ingredient)
 
 # Register core models we need in our tests
 from django.contrib.auth.models import User, Group

tests/admin_views/models.py

@@ -852,3 +852,13 @@ class InlineReference(models.Model):
 
 class InlineReferer(models.Model):
     refs = models.ManyToManyField(InlineReference)
+
+
+# Models for #23604
+class Recipe(models.Model):
+    name = models.CharField(max_length=20)
+
+
+class Ingredient(models.Model):
+    name = models.CharField(max_length=20)
+    recipes = models.ManyToManyField('Recipe', related_name='ingredients')

tests/admin_views/tests.py

@@ -621,6 +621,10 @@ class AdminViewBasicTest(AdminViewBasicTestCase):
         response = self.client.get("/test_admin/admin/admin_views/m2mreference/", {TO_FIELD_VAR: 'id'})
         self.assertEqual(response.status_code, 200)
 
+        # #23604 - Specifying the pk of this model should be allowed when this model defines a m2m relationship
+        response = self.client.get("/test_admin/admin/admin_views/ingredient/", {TO_FIELD_VAR: 'id'})
+        self.assertEqual(response.status_code, 200)
+
         # #23329 - Specifying a field that is not refered by any other model directly registered
         # to this admin site but registered through inheritance should be allowed.
         response = self.client.get("/test_admin/admin/admin_views/referencedbyparent/", {TO_FIELD_VAR: 'id'})