Fixed #25606 -- Added support for "__" lookup in RelatedOnlyFieldList

django/contrib/admin/filters.py

@@ -166,9 +166,9 @@ class RelatedFieldListFilter(FieldListFilter):
         self.lookup_kwarg_isnull = '%s__isnull' % field_path
         self.lookup_val = request.GET.get(self.lookup_kwarg)
         self.lookup_val_isnull = request.GET.get(self.lookup_kwarg_isnull)
-        self.lookup_choices = self.field_choices(field, request, model_admin)
         super(RelatedFieldListFilter, self).__init__(
             field, request, params, model, model_admin, field_path)
+        self.lookup_choices = self.field_choices(field, request, model_admin)
         if hasattr(field, 'verbose_name'):
             self.lookup_title = field.verbose_name
         else:
@@ -412,5 +412,5 @@ FieldListFilter.register(lambda f: True, AllValuesFieldListFilter)
 
 class RelatedOnlyFieldListFilter(RelatedFieldListFilter):
     def field_choices(self, field, request, model_admin):
-        limit_choices_to = {'pk__in': set(model_admin.get_queryset(request).values_list(field.name, flat=True))}
-        return field.get_choices(include_blank=False, limit_choices_to=limit_choices_to)
+        pk_qs = model_admin.get_queryset(request).distinct().values_list('%s__pk' % self.field_path, flat=True)
+        return field.get_choices(include_blank=False, limit_choices_to={'pk__in': pk_qs})

tests/admin_filters/models.py

@@ -26,6 +26,12 @@ class Book(models.Model):
         related_name='books_contributed',
         blank=True,
     )
+    employee = models.ForeignKey(
+        'Employee',
+        models.SET_NULL,
+        verbose_name='Employee',
+        blank=True, null=True,
+    )
     is_best_seller = models.NullBooleanField(default=0)
     date_registered = models.DateField(null=True)
     # This field name is intentionally 2 characters long (#16080).

tests/admin_filters/tests.py

@@ -169,6 +169,7 @@ class BookAdminRelatedOnlyFilter(ModelAdmin):
         'year', 'is_best_seller', 'date_registered', 'no',
         ('author', RelatedOnlyFieldListFilter),
         ('contributors', RelatedOnlyFieldListFilter),
+        ('employee__department', RelatedOnlyFieldListFilter),
     )
     ordering = ('-id',)
 
@@ -580,6 +581,26 @@ class ListFiltersTests(TestCase):
         expected = [(self.alfred.pk, 'alfred'), (self.bob.pk, 'bob')]
         self.assertEqual(sorted(filterspec.lookup_choices), sorted(expected))
 
+    def test_relatedonlyfieldlistfilter_underscorelookup_foreignkey(self):
+        Department.objects.create(code='TEST', description='Testing')
+        self.djangonaut_book.employee = self.john
+        self.djangonaut_book.save()
+        self.bio_book.employee = self.jack
+        self.bio_book.save()
+
+        modeladmin = BookAdminRelatedOnlyFilter(Book, site)
+        request = self.request_factory.get('/')
+        changelist = self.get_changelist(request, Book, modeladmin)
+
+        # Only actual departments should be present in employee__department's
+        # list filter.
+        filterspec = changelist.get_filters(request)[0][6]
+        expected = [
+            (self.dev.code, str(self.dev)),
+            (self.design.code, str(self.design)),
+        ]
+        self.assertEqual(sorted(filterspec.lookup_choices), sorted(expected))
+
     def test_relatedonlyfieldlistfilter_manytomany(self):
         modeladmin = BookAdminRelatedOnlyFilter(Book, site)