Fixed #27998 -- Made ManyToManyField changes logged in admin's object history.

AUTHORS

@@ -468,6 +468,7 @@ answer newbie questions, and generally made Django that much better:
     Lex Berezhny <lex@damoti.com>
     Liang Feng <hutuworm@gmail.com>
     limodou
+    Lincoln Smith <lincoln.smith@anu.edu.au>
     Loek van Gent <loek@barakken.nl>
     Loïc Bistuer <loic.bistuer@sixmedia.com>
     Lowe Thiderman <lowe.thiderman@gmail.com>

django/contrib/admin/options.py

@@ -1442,6 +1442,10 @@ class ModelAdmin(BaseModelAdmin):
                 new_object = form.instance
             formsets, inline_instances = self._create_formsets(request, new_object, change=not add)
             if all_valid(formsets) and form_validated:
+                if not add:
+                    # Evalute querysets in form.initial so that changes to
+                    # ManyToManyFields are reflected in this change's LogEntry.
+                    form.has_changed()
                 self.save_model(request, new_object, form, not add)
                 self.save_related(request, form, formsets, not add)
                 change_message = self.construct_change_message(request, form, formsets, add)

tests/admin_views/admin.py

@@ -35,14 +35,14 @@ from .models import (
     OtherStory, Paper, Parent, ParentWithDependentChildren, ParentWithUUIDPK,
     Person, Persona, Picture, Pizza, Plot, PlotDetails, PlotProxy,
     PluggableSearchPerson, Podcast, Post, PrePopulatedPost,
-    PrePopulatedPostLargeSlug, PrePopulatedSubPost, Promo, Question, Recipe,
+    PrePopulatedPostLargeSlug, PrePopulatedSubPost, Promo, Question,
-    Recommendation, Recommender, ReferencedByGenRel, ReferencedByInline,
+    ReadablePizza, Recipe, Recommendation, Recommender, ReferencedByGenRel,
-    ReferencedByParent, RelatedPrepopulated, RelatedWithUUIDPKModel, Report,
+    ReferencedByInline, ReferencedByParent, RelatedPrepopulated,
-    Reservation, Restaurant, RowLevelChangePermissionModel, Section,
+    RelatedWithUUIDPKModel, Report, Reservation, Restaurant,
-    ShortMessage, Simple, Sketch, State, Story, StumpJoke, Subscriber,
+    RowLevelChangePermissionModel, Section, ShortMessage, Simple, Sketch,
-    SuperVillain, Telegram, Thing, Topping, UnchangeableObject,
+    State, Story, StumpJoke, Subscriber, SuperVillain, Telegram, Thing,
-    UndeletableObject, UnorderedObject, UserMessenger, Villain, Vodcast,
+    Topping, UnchangeableObject, UndeletableObject, UnorderedObject,
-    Whatsit, Widget, Worker, WorkHour,
+    UserMessenger, Villain, Vodcast, Whatsit, Widget, Worker, WorkHour,
 )
 
 
@@ -970,6 +970,7 @@ site.register(Book, inlines=[ChapterInline])
 site.register(Promo)
 site.register(ChapterXtra1, ChapterXtra1Admin)
 site.register(Pizza, PizzaAdmin)
+site.register(ReadablePizza)
 site.register(Topping, ToppingAdmin)
 site.register(Album, AlbumAdmin)
 site.register(Question)

tests/admin_views/models.py

@@ -575,6 +575,13 @@ class Pizza(models.Model):
     toppings = models.ManyToManyField('Topping', related_name='pizzas')
 
 
+# Pizza's ModelAdmin has readonly_fields = ['toppings'].
+# toppings is editable for this model's admin.
+class ReadablePizza(Pizza):
+    class Meta:
+        proxy = True
+
+
 class Album(models.Model):
     owner = models.ForeignKey(User, models.SET_NULL, null=True, blank=True)
     title = models.CharField(max_length=30)

tests/admin_views/tests.py

@@ -54,12 +54,13 @@ from .models import (
     ModelWithStringPrimaryKey, OtherStory, Paper, Parent,
     ParentWithDependentChildren, ParentWithUUIDPK, Person, Persona, Picture,
     Pizza, Plot, PlotDetails, PluggableSearchPerson, Podcast, Post,
-    PrePopulatedPost, Promo, Question, Recommendation, Recommender,
+    PrePopulatedPost, Promo, Question, ReadablePizza, Recommendation,
-    RelatedPrepopulated, RelatedWithUUIDPKModel, Report, Restaurant,
+    Recommender, RelatedPrepopulated, RelatedWithUUIDPKModel, Report,
-    RowLevelChangePermissionModel, SecretHideout, Section, ShortMessage,
+    Restaurant, RowLevelChangePermissionModel, SecretHideout, Section,
-    Simple, State, Story, Subscriber, SuperSecretHideout, SuperVillain,
+    ShortMessage, Simple, State, Story, Subscriber, SuperSecretHideout,
-    Telegram, TitleTranslation, Topping, UnchangeableObject, UndeletableObject,
+    SuperVillain, Telegram, TitleTranslation, Topping, UnchangeableObject,
-    UnorderedObject, Villain, Vodcast, Whatsit, Widget, Worker, WorkHour,
+    UndeletableObject, UnorderedObject, Villain, Vodcast, Whatsit, Widget,
+    Worker, WorkHour,
 )
 
 
@@ -876,6 +877,17 @@ class AdminViewBasicTest(AdminViewBasicTestCase):
         response = self.client.get(reverse('admin:admin_views_undeletableobject_change', args=(instance.pk,)))
         self.assertNotContains(response, 'deletelink')
 
+    def test_change_view_logs_m2m_field_changes(self):
+        """Changes to ManyToManyFields are included in the object's history."""
+        pizza = ReadablePizza.objects.create(name='Cheese')
+        cheese = Topping.objects.create(name='cheese')
+        post_data = {'name': pizza.name, 'toppings': [cheese.pk]}
+        response = self.client.post(reverse('admin:admin_views_readablepizza_change', args=(pizza.pk,)), post_data)
+        self.assertRedirects(response, reverse('admin:admin_views_readablepizza_changelist'))
+        pizza_ctype = ContentType.objects.get_for_model(ReadablePizza, for_concrete_model=False)
+        log = LogEntry.objects.filter(content_type=pizza_ctype, object_id=pizza.pk).first()
+        self.assertEqual(log.get_change_message(), 'Changed toppings.')
+
     def test_allows_attributeerror_to_bubble_up(self):
         """
         AttributeErrors are allowed to bubble when raised inside a change list