[1.6.x] Fixed #21405 -- Prevented queryset overwrite in BaseModelAdmin

Thanks guido@20tab.com for the report and Tim Graham for the
analyze.
Backport of 1718b5256c from master.

3 files changed, 32 insertions, 6 deletions

diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index a841ee30b9..9dddcb0dfb 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -209,9 +209,10 @@ class BaseModelAdmin(six.with_metaclass(RenameBaseModelAdminMethods)):
             })
             kwargs['empty_label'] = _('None') if db_field.blank else None
 
-        queryset = self.get_field_queryset(db, db_field, request)
-        if queryset is not None:
-            kwargs['queryset'] = queryset
+        if not 'queryset' in kwargs:
+            queryset = self.get_field_queryset(db, db_field, request)
+            if queryset is not None:
+                kwargs['queryset'] = queryset
 
         return db_field.formfield(**kwargs)
 
@@ -232,9 +233,10 @@ class BaseModelAdmin(six.with_metaclass(RenameBaseModelAdminMethods)):
         elif db_field.name in (list(self.filter_vertical) + list(self.filter_horizontal)):
             kwargs['widget'] = widgets.FilteredSelectMultiple(db_field.verbose_name, (db_field.name in self.filter_vertical))
 
-        queryset = self.get_field_queryset(db, db_field, request)
-        if queryset is not None:
-            kwargs['queryset'] = queryset
+        if not 'queryset' in kwargs:
+            queryset = self.get_field_queryset(db, db_field, request)
+            if queryset is not None:
+                kwargs['queryset'] = queryset
 
         return db_field.formfield(**kwargs)
 
diff --git a/docs/releases/1.6.1.txt b/docs/releases/1.6.1.txt
index d7f73903ff..db05bcdca2 100644
--- a/docs/releases/1.6.1.txt
+++ b/docs/releases/1.6.1.txt
@@ -28,3 +28,5 @@ Bug fixes
   non related to file extensions (#21457).
 * Fixed display of inline instances in formsets when parent has 0 for primary
   key (#21472).
+* Fixed a regression where custom querysets for foreign keys were overwritten
+  if ``ModelAdmin`` had ordering set (#21405).
diff --git a/tests/admin_ordering/tests.py b/tests/admin_ordering/tests.py
index 6655ad37ad..083c053d66 100644
--- a/tests/admin_ordering/tests.py
+++ b/tests/admin_ordering/tests.py
@@ -148,6 +148,28 @@ class TestRelatedFieldsAdminOrdering(TestCase):
         # should be ordered by rank (defined by the ModelAdmin)
         self.check_ordering_of_field_choices([self.b1, self.b2])
 
+    def test_custom_queryset_still_wins(self):
+        """Test that custom queryset has still precedence (#21405)"""
+        class SongAdmin(admin.ModelAdmin):
+            # Exclude one of the two Bands from the querysets
+            def formfield_for_foreignkey(self, db_field, **kwargs):
+                if db_field.name == 'band':
+                    kwargs["queryset"] = Band.objects.filter(rank__gt=2)
+                return super(SongAdmin, self).formfield_for_foreignkey(db_field, **kwargs)
+            def formfield_for_manytomany(self, db_field, **kwargs):
+                if db_field.name == 'other_interpreters':
+                    kwargs["queryset"] = Band.objects.filter(rank__gt=2)
+                return super(SongAdmin, self).formfield_for_foreignkey(db_field, **kwargs)
+
+        class StaticOrderingBandAdmin(admin.ModelAdmin):
+            ordering = ('rank',)
+
+        admin.site.unregister(Song)
+        admin.site.register(Song, SongAdmin)
+        admin.site.register(Band, StaticOrderingBandAdmin)
+
+        self.check_ordering_of_field_choices([self.b2])
+
     def tearDown(self):
         admin.site.unregister(Song)
         if Band in admin.site._registry: