fix: migrations created_by (#1712)

* fix: migrations created_by

* added list comprehension

* huddle

aimmo/migrations/0030_update_created_by.py

@@ -5,10 +5,8 @@
 def populate_created_by(apps, schema_editor):
     Game = apps.get_model("aimmo", "Game")
     db_alias = schema_editor.connection.alias
-    games = Game.objects.using(db_alias).all()
-    for game in games:
-        if not game.created_by:
-            game.created_by = game.owner
+    games = Game.objects.using(db_alias).filter(created_by=None).exclude(owner=None)
+    [Game.objects.using(db_alias).filter(id=game.id).update(created_by=game.owner.new_teacher) for game in games]
 
 
 class Migration(migrations.Migration):