Fixed #36674 -- Fixed memory leak in select_related().

django/db/models/sql/compiler.py

@@ -228,6 +228,13 @@ class SQLCompiler:
             ]
         return expressions
 
+    @classmethod
+    def get_select_from_parent(cls, klass_info):
+        for ki in klass_info["related_klass_infos"]:
+            if ki["from_parent"]:
+                ki["select_fields"] = klass_info["select_fields"] + ki["select_fields"]
+            cls.get_select_from_parent(ki)
+
     def get_select(self, with_col_aliases=False):
         """
         Return three values:
@@ -300,15 +307,7 @@ class SQLCompiler:
             related_klass_infos = self.get_related_selections(select, select_mask)
             klass_info["related_klass_infos"] = related_klass_infos
 
-            def get_select_from_parent(klass_info):
-                for ki in klass_info["related_klass_infos"]:
-                    if ki["from_parent"]:
-                        ki["select_fields"] = (
-                            klass_info["select_fields"] + ki["select_fields"]
-                        )
-                    get_select_from_parent(ki)
-
-            get_select_from_parent(klass_info)
+            self.get_select_from_parent(klass_info)
 
         ret = []
         col_idx = 1

tests/select_related/tests.py

@@ -1,6 +1,9 @@
+import gc
+
 from django.core.exceptions import FieldError
 from django.db.models import FETCH_PEERS
 from django.test import SimpleTestCase, TestCase
+from django.test.utils import garbage_collect
 
 from .models import (
     Bookmark,
@@ -57,6 +60,17 @@ class SelectRelatedTests(TestCase):
             "Amanita muscaria"
         )
 
+    def setup_gc_debug(self):
+        self.addCleanup(gc.set_debug, 0)
+        self.addCleanup(gc.enable)
+        gc.disable()
+        garbage_collect()
+        gc.set_debug(gc.DEBUG_SAVEALL)
+
+    def assert_no_memory_leaks(self):
+        garbage_collect()
+        self.assertEqual(gc.garbage, [])
+
     def test_access_fks_without_select_related(self):
         """
         Normally, accessing FKs doesn't fill in related objects
@@ -128,6 +142,11 @@ class SelectRelatedTests(TestCase):
         )
         self.assertEqual(s.id + 10, s.a)
 
+    def test_select_related_memory_leak(self):
+        self.setup_gc_debug()
+        list(Species.objects.select_related("genus"))
+        self.assert_no_memory_leaks()
+
     def test_certain_fields(self):
         """
         The optional fields passed to select_related() control which related