[1.8.x] Fixed #26060 -- Fixed crash with reverse OneToOneField in ModelAdmin.readonly_fields.

Backport of 9a33d3d764 from master

django/contrib/admin/helpers.py

@@ -203,7 +203,7 @@ class AdminReadonlyField(object):
                     else:
                         result_repr = linebreaksbr(result_repr)
             else:
-                if isinstance(f.rel, ManyToManyRel) and value is not None:
+                if isinstance(getattr(f, 'rel', None), ManyToManyRel) and value is not None:
                     result_repr = ", ".join(map(six.text_type, value.all()))
                 else:
                     result_repr = display_for_field(value, f)

django/contrib/admin/utils.py

@@ -376,7 +376,7 @@ def display_for_field(value, field):
     from django.contrib.admin.templatetags.admin_list import _boolean_icon
     from django.contrib.admin.views.main import EMPTY_CHANGELIST_VALUE
 
-    if field.flatchoices:
+    if getattr(field, 'flatchoices', None):
         return dict(field.flatchoices).get(value, EMPTY_CHANGELIST_VALUE)
     # NullBooleanField needs special-case null-handling, so it comes
     # before the general null test.

docs/releases/1.8.9.txt

@@ -26,3 +26,6 @@ Bugfixes
 
 * Fixed a crash when using an ``__in`` lookup inside a ``Case`` expression
   (:ticket:`26071`).
+
+* Fixed a crash when using a reverse ``OneToOneField`` in
+  ``ModelAdmin.readonly_fields`` (:ticket:`26060`).

tests/admin_views/admin.py

@@ -34,15 +34,15 @@ from .models import (
     InlineReference, InlineReferer, Inquisition, Language, Link,
     MainPrepopulated, ModelWithStringPrimaryKey, NotReferenced, OldSubscriber,
     OtherStory, Paper, Parent, ParentWithDependentChildren, Person, Persona,
-    Picture, Pizza, Plot, PlotDetails, PluggableSearchPerson, Podcast, Post,
-    PrePopulatedPost, PrePopulatedPostLargeSlug, PrePopulatedSubPost, Promo,
-    Question, Recipe, Recommendation, Recommender, ReferencedByGenRel,
-    ReferencedByInline, ReferencedByParent, RelatedPrepopulated, Report,
-    Reservation, Restaurant, RowLevelChangePermissionModel, Section,
-    ShortMessage, Simple, Sketch, State, Story, StumpJoke, Subscriber,
-    SuperVillain, Telegram, Thing, Topping, UnchangeableObject,
-    UndeletableObject, UnorderedObject, UserMessenger, Villain, Vodcast,
-    Whatsit, Widget, Worker, WorkHour,
+    Picture, Pizza, Plot, PlotDetails, PlotProxy, PluggableSearchPerson,
+    Podcast, Post, PrePopulatedPost, PrePopulatedPostLargeSlug,
+    PrePopulatedSubPost, Promo, Question, Recipe, Recommendation, Recommender,
+    ReferencedByGenRel, ReferencedByInline, ReferencedByParent,
+    RelatedPrepopulated, Report, Reservation, Restaurant,
+    RowLevelChangePermissionModel, Section, ShortMessage, Simple, Sketch,
+    State, Story, StumpJoke, Subscriber, SuperVillain, Telegram, Thing,
+    Topping, UnchangeableObject, UndeletableObject, UnorderedObject,
+    UserMessenger, Villain, Vodcast, Whatsit, Widget, Worker, WorkHour,
 )
 
 
@@ -853,6 +853,10 @@ class InlineRefererAdmin(admin.ModelAdmin):
     inlines = [InlineReferenceInline]
 
 
+class PlotReadonlyAdmin(admin.ModelAdmin):
+    readonly_fields = ('plotdetails',)
+
+
 class GetFormsetsArgumentCheckingAdmin(admin.ModelAdmin):
     fields = ['name']
 
@@ -907,6 +911,7 @@ site.register(Villain)
 site.register(SuperVillain)
 site.register(Plot)
 site.register(PlotDetails)
+site.register(PlotProxy, PlotReadonlyAdmin)
 site.register(CyclicOne)
 site.register(CyclicTwo)
 site.register(WorkHour, WorkHourAdmin)

tests/admin_views/models.py

@@ -501,12 +501,17 @@ class Plot(models.Model):
 @python_2_unicode_compatible
 class PlotDetails(models.Model):
     details = models.CharField(max_length=100)
-    plot = models.OneToOneField(Plot)
+    plot = models.OneToOneField(Plot, null=True, blank=True)
 
     def __str__(self):
         return self.details
 
 
+class PlotProxy(Plot):
+    class Meta:
+        proxy = True
+
+
 @python_2_unicode_compatible
 class SecretHideout(models.Model):
     """ Secret! Not registered with the admin! """

tests/admin_views/tests.py

@@ -52,11 +52,11 @@ from .models import (
     FoodDelivery, FunkyTag, Gallery, Grommet, Inquisition, Language, Link,
     MainPrepopulated, ModelWithStringPrimaryKey, OtherStory, Paper, Parent,
     ParentWithDependentChildren, Person, Persona, Picture, Pizza, Plot,
-    PluggableSearchPerson, Podcast, Post, Promo, Question, RelatedPrepopulated,
-    Report, Restaurant, RowLevelChangePermissionModel, Section, ShortMessage,
-    Simple, Story, Subscriber, Telegram, Topping, UnchangeableObject,
-    UndeletableObject, UnorderedObject, Vodcast, Whatsit, Widget, Worker,
-    WorkHour,
+    PlotDetails, PluggableSearchPerson, Podcast, Post, Promo, Question,
+    RelatedPrepopulated, Report, Restaurant, RowLevelChangePermissionModel,
+    Section, ShortMessage, Simple, Story, Subscriber, Telegram, Topping,
+    UnchangeableObject, UndeletableObject, UnorderedObject, Villain, Vodcast,
+    Whatsit, Widget, Worker, WorkHour,
 )
 
 
@@ -64,6 +64,44 @@ ERROR_MESSAGE = "Please enter the correct username and password \
 for a staff account. Note that both fields may be case-sensitive."
 
 
+class AdminFieldExtractionMixin(object):
+    """
+    Helper methods for extracting data from AdminForm.
+    """
+    def get_admin_form_fields(self, response):
+        """
+        Return a list of AdminFields for the AdminForm in the response.
+        """
+        admin_form = response.context['adminform']
+        fieldsets = list(admin_form)
+
+        field_lines = []
+        for fieldset in fieldsets:
+            field_lines += list(fieldset)
+
+        fields = []
+        for field_line in field_lines:
+            fields += list(field_line)
+
+        return fields
+
+    def get_admin_fields(self, response):
+        """
+        Return the fields for the response's AdminForm.
+        """
+        return [f for f in self.get_admin_form_fields(response)]
+
+    def get_admin_field(self, response, field_name):
+        """
+        Return the field for the given field_name.
+        """
+        fields = self.get_admin_fields(response)
+        for field in fields:
+            name = field.field['name'] if isinstance(field.field, dict) else field.field.name
+            if name == field_name:
+                return field
+
+
 @override_settings(PASSWORD_HASHERS=('django.contrib.auth.hashers.SHA1PasswordHasher',),
                    ROOT_URLCONF="admin_views.urls",
                    USE_I18N=True, USE_L10N=False, LANGUAGE_CODE='en')
@@ -4029,7 +4067,7 @@ class SeleniumAdminViewsIETests(SeleniumAdminViewsFirefoxTests):
 
 @override_settings(PASSWORD_HASHERS=('django.contrib.auth.hashers.SHA1PasswordHasher',),
     ROOT_URLCONF="admin_views.urls")
-class ReadonlyTest(TestCase):
+class ReadonlyTest(AdminFieldExtractionMixin, TestCase):
     fixtures = ['admin-views-users.xml']
 
     def setUp(self):
@@ -4126,7 +4164,7 @@ class ReadonlyTest(TestCase):
         self.assertContains(response, '<p>No opinion</p>', html=True)
         self.assertNotContains(response, '<p>(None)</p>')
 
-    def test_readonly_backwards_ref(self):
+    def test_readonly_manytomany_backwards_ref(self):
         """
         Regression test for #16433 - backwards references for related objects
         broke if the related field is read-only due to the help_text attribute
@@ -4137,6 +4175,26 @@ class ReadonlyTest(TestCase):
         response = self.client.get(reverse('admin:admin_views_topping_add'))
         self.assertEqual(response.status_code, 200)
 
+    def test_readonly_onetoone_backwards_ref(self):
+        """
+        Can reference a reverse OneToOneField in ModelAdmin.readonly_fields.
+        """
+        v1 = Villain.objects.create(name='Adam')
+        pl = Plot.objects.create(name='Test Plot', team_leader=v1, contact=v1)
+        pd = PlotDetails.objects.create(details='Brand New Plot', plot=pl)
+
+        response = self.client.get(reverse('admin:admin_views_plotproxy_change', args=(pl.pk,)))
+        field = self.get_admin_field(response, 'plotdetails')
+        self.assertEqual(field.contents(), 'Brand New Plot')
+
+        # The reverse relation also works if the OneToOneField is null.
+        pd.plot = None
+        pd.save()
+
+        response = self.client.get(reverse('admin:admin_views_plotproxy_change', args=(pl.pk,)))
+        field = self.get_admin_field(response, 'plotdetails')
+        self.assertEqual(force_text(field.contents()), '(None)')
+
     def test_readonly_field_overrides(self):
         """
         Regression test for #22087 - ModelForm Meta overrides are ignored by