Fixed #23915 -- Made sure m2m fields through non-pk to_field are allowed in the admin.

refs #23754, #23862

django/contrib/admin/options.py

@@ -459,6 +459,12 @@ class BaseModelAdmin(six.with_metaclass(forms.MediaDefiningClass)):
         if field.primary_key:
             return True
 
+        # Allow reverse relationships to models defining m2m fields if they
+        # target the specified field.
+        for many_to_many in opts.many_to_many:
+            if many_to_many.m2m_target_field_name() == to_field:
+                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()
@@ -467,7 +473,8 @@ class BaseModelAdmin(six.with_metaclass(forms.MediaDefiningClass)):
             for inline in admin.inlines:
                 registered_models.add(inline.model)
 
-        for related_object in opts.get_all_related_objects(include_hidden=True):
+        for related_object in (opts.get_all_related_objects(include_hidden=True) +
+                               opts.get_all_related_many_to_many_objects()):
             related_model = related_object.model
             if (any(issubclass(model, related_model) for model in registered_models) and
                     related_object.field.rel.get_related_field() == field):

tests/admin_views/models.py

@@ -855,13 +855,19 @@ class InlineReferer(models.Model):
     refs = models.ManyToManyField(InlineReference)
 
 
-# Models for #23604
+# Models for #23604 and #23915
 class Recipe(models.Model):
-    pass
+    rname = models.CharField(max_length=20, unique=True)
 
 
 class Ingredient(models.Model):
-    recipes = models.ManyToManyField(Recipe)
+    iname = models.CharField(max_length=20, unique=True)
+    recipes = models.ManyToManyField(Recipe, through='RecipeIngredient')
+
+
+class RecipeIngredient(models.Model):
+    ingredient = models.ForeignKey(Ingredient, to_field='iname')
+    recipe = models.ForeignKey(Recipe, to_field='rname')
 
 
 # Model for #23839

tests/admin_views/tests.py

@@ -616,16 +616,12 @@ class AdminViewBasicTest(AdminViewBasicTestCase):
         response = self.client.get("/test_admin/admin/admin_views/notreferenced/", {TO_FIELD_VAR: 'id'})
         self.assertEqual(response.status_code, 200)
 
-        # Specifying a field referenced by another model though a m2m should be allowed.
+        # #23915 - Specifying a field referenced by another model though a m2m should be allowed.
-        # XXX: We're not testing against a non-primary key field since the admin doesn't
+        response = self.client.get("/test_admin/admin/admin_views/recipe/", {TO_FIELD_VAR: 'rname'})
-        # support it yet, ref #23862
-        response = self.client.get("/test_admin/admin/admin_views/recipe/", {TO_FIELD_VAR: 'id'})
         self.assertEqual(response.status_code, 200)
 
-        # #23604 - Specifying a field referenced through a reverse m2m relationship should be allowed.
+        # #23604, #23915 - Specifying a field referenced through a reverse m2m relationship should be allowed.
-        # XXX: We're not testing against a non-primary key field since the admin doesn't
+        response = self.client.get("/test_admin/admin/admin_views/ingredient/", {TO_FIELD_VAR: 'iname'})
-        # support it yet, ref #23862
-        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 referred by any other model directly registered