Fixed #26060 -- Fixed crash with reverse OneToOneField in ModelAdmin.readonly_fields.

django/contrib/admin/utils.py

@@ -383,7 +383,7 @@ def help_text_for_field(name, model):
 def display_for_field(value, field, empty_value_display):
     from django.contrib.admin.templatetags.admin_list import _boolean_icon
 
-    if field.flatchoices:
+    if getattr(field, 'flatchoices', None):
         return dict(field.flatchoices).get(value, empty_value_display)
     # 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`).

docs/releases/1.9.2.txt

@@ -49,3 +49,6 @@ Bugfixes
   SQLite with more than 2000 parameters when :setting:`DEBUG` is ``True`` on
   distributions that increase the ``SQLITE_MAX_VARIABLE_NUMBER`` compile-time
   limit to over 2000, such as Debian (:ticket:`26063`).
+
+* Fixed a crash when using a reverse ``OneToOneField`` in
+  ``ModelAdmin.readonly_fields`` (:ticket:`26060`).

tests/admin_views/admin.py

@@ -35,15 +35,16 @@ from .models import (
     InlineReference, InlineReferer, Inquisition, Language, Link,
     MainPrepopulated, ModelWithStringPrimaryKey, NotReferenced, OldSubscriber,
     OtherStory, Paper, Parent, ParentWithDependentChildren, ParentWithUUIDPK,
-    Person, Persona, Picture, Pizza, Plot, PlotDetails, PluggableSearchPerson,
-    Podcast, Post, PrePopulatedPost, PrePopulatedPostLargeSlug,
-    PrePopulatedSubPost, Promo, Question, Recipe, Recommendation, Recommender,
-    ReferencedByGenRel, ReferencedByInline, ReferencedByParent,
-    RelatedPrepopulated, RelatedWithUUIDPKModel, 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,
+    Person, Persona, Picture, Pizza, Plot, PlotDetails, PlotProxy,
+    PluggableSearchPerson, Podcast, Post, PrePopulatedPost,
+    PrePopulatedPostLargeSlug, PrePopulatedSubPost, Promo, Question, Recipe,
+    Recommendation, Recommender, ReferencedByGenRel, ReferencedByInline,
+    ReferencedByParent, RelatedPrepopulated, RelatedWithUUIDPKModel, 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,
 )
 
 
@@ -866,6 +867,10 @@ class InlineRefererAdmin(admin.ModelAdmin):
     inlines = [InlineReferenceInline]
 
 
+class PlotReadonlyAdmin(admin.ModelAdmin):
+    readonly_fields = ('plotdetails',)
+
+
 class GetFormsetsArgumentCheckingAdmin(admin.ModelAdmin):
     fields = ['name']
 
@@ -920,6 +925,7 @@ site.register(Villain)
 site.register(SuperVillain)
 site.register(Plot)
 site.register(PlotDetails)
+site.register(PlotProxy, PlotReadonlyAdmin)
 site.register(Bookmark)
 site.register(CyclicOne)
 site.register(CyclicTwo)

tests/admin_views/models.py

@@ -538,12 +538,17 @@ class Plot(models.Model):
 @python_2_unicode_compatible
 class PlotDetails(models.Model):
     details = models.CharField(max_length=100)
-    plot = models.OneToOneField(Plot, models.CASCADE)
+    plot = models.OneToOneField(Plot, models.CASCADE, 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

@@ -67,6 +67,43 @@ 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_readonly_fields(self, response):
+        """
+        Return the readonly fields for the response's AdminForm.
+        """
+        return [f for f in self.get_admin_form_fields(response) if f.is_readonly]
+
+    def get_admin_readonly_field(self, response, field_name):
+        """
+        Return the readonly field for the given field_name.
+        """
+        admin_readonly_fields = self.get_admin_readonly_fields(response)
+        for field in admin_readonly_fields:
+            if field.field['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')
@@ -4556,7 +4593,7 @@ class SeleniumAdminViewsIETests(SeleniumAdminViewsFirefoxTests):
 
 @override_settings(PASSWORD_HASHERS=['django.contrib.auth.hashers.SHA1PasswordHasher'],
     ROOT_URLCONF="admin_views.urls")
-class ReadonlyTest(TestCase):
+class ReadonlyTest(AdminFieldExtractionMixin, TestCase):
 
     @classmethod
     def setUpTestData(cls):
@@ -4677,7 +4714,7 @@ 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
@@ -4688,6 +4725,26 @@ 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_readonly_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_readonly_field(response, 'plotdetails')
+        self.assertEqual(field.contents(), '-')  # default empty value
+
     @ignore_warnings(category=RemovedInDjango20Warning)  # for allow_tags deprecation
     def test_readonly_field_overrides(self):
         """