[3.0.x] Fixed #30854 -- Fixed QuerySet.select_related() with multiple FilteredRelations.

Backport of 6a75cea76a from master.

django/db/models/sql/compiler.py

@@ -1,6 +1,7 @@
 import collections
 import re
 import warnings
+from functools import partial
 from itertools import chain
 
 from django.core.exceptions import EmptyResultSet, FieldError
@@ -902,6 +903,10 @@ class SQLCompiler:
                     select, model._meta, alias, cur_depth + 1,
                     next, restricted)
                 get_related_klass_infos(klass_info, next_klass_infos)
+
+            def remote_setter(name, obj, from_obj):
+                setattr(from_obj, name, obj)
+
             for name in list(requested):
                 # Filtered relations work only on the topmost level.
                 if cur_depth > 1:
@@ -917,15 +922,12 @@ class SQLCompiler:
                         # Set a reverse fk object when relation is non-empty.
                         if from_obj:
                             f.remote_field.set_cached_value(from_obj, obj)
-
-                    def remote_setter(obj, from_obj):
-                        setattr(from_obj, name, obj)
                     klass_info = {
                         'model': model,
                         'field': f,
                         'reverse': True,
                         'local_setter': local_setter,
-                        'remote_setter': remote_setter,
+                        'remote_setter': partial(remote_setter, name),
                         'from_parent': from_parent,
                     }
                     related_klass_infos.append(klass_info)

tests/filtered_relation/tests.py

@@ -50,6 +50,18 @@ class FilteredRelationTests(TestCase):
                 (self.author2, self.book3, self.editor_b, self.author2),
             ], lambda x: (x, x.book_join, x.book_join.editor, x.book_join.author))
 
+    def test_select_related_multiple(self):
+        qs = Book.objects.annotate(
+            author_join=FilteredRelation('author'),
+            editor_join=FilteredRelation('editor'),
+        ).select_related('author_join', 'editor_join').order_by('pk')
+        self.assertQuerysetEqual(qs, [
+            (self.book1, self.author1, self.editor_a),
+            (self.book2, self.author2, self.editor_b),
+            (self.book3, self.author2, self.editor_b),
+            (self.book4, self.author1, self.editor_a),
+        ], lambda x: (x, x.author_join, x.editor_join))
+
     def test_select_related_with_empty_relation(self):
         qs = Author.objects.annotate(
             book_join=FilteredRelation('book', condition=Q(pk=-1)),