Fix signals interfering with deleting a game with sessions

games/signals.py

@@ -20,7 +20,15 @@ def update_num_purchases(sender, instance, **kwargs):
 
 @receiver([post_save, post_delete], sender=Session)
 def update_game_playtime(sender, instance, **kwargs):
-    game = instance.game
+    # During cascade deletes the related Game may already have been removed.
+    # Use the FK id to look up the Game safely and bail out if it no longer exists.
+    game_pk = getattr(instance, "game_id", None)
+    if not game_pk:
+        return
+    game = Game.objects.filter(pk=game_pk).first()
+    if not game:
+        return
+
     total_playtime = game.sessions.aggregate(
         total_playtime=Sum(F("duration_calculated") + F("duration_manual"))
     )["total_playtime"]

tests/test_signals.py

@@ -0,0 +1,39 @@
+import os
+from datetime import datetime
+from zoneinfo import ZoneInfo
+
+import django
+from django.test import TestCase
+
+os.environ.setdefault("DJANGO_SETTINGS_MODULE", "timetracker.settings")
+django.setup()
+from django.conf import settings
+
+from games.models import Game, Session
+
+ZONEINFO = ZoneInfo(settings.TIME_ZONE)
+
+
+class SignalsTest(TestCase):
+    def test_deleting_game_with_sessions_does_not_raise(self):
+        # Create a game and attach a session to it
+        g = Game(name="Signal Test Game")
+        g.save()
+
+        s = Session(
+            game=g,
+            timestamp_start=datetime(2022, 9, 26, 14, 58, tzinfo=ZONEINFO),
+            timestamp_end=datetime(2022, 9, 26, 17, 38, tzinfo=ZONEINFO),
+        )
+        s.save()
+
+        # Sanity checks before delete
+        self.assertTrue(Game.objects.filter(pk=g.pk).exists())
+        self.assertEqual(g.sessions.count(), 1)
+
+        # Deleting the game should not raise (signals run during cascade)
+        g.delete()
+
+        # After deletion, the Game should be gone and no sessions remain
+        self.assertFalse(Game.objects.filter(pk=g.pk).exists())
+        self.assertEqual(Session.objects.filter(pk=s.pk).count(), 0)