Fix creating to many ScheduledMails on subevent creation (#4620)

src/pretix/plugins/sendmail/migrations/008_remove_scheduled_mails.py

@@ -0,0 +1,19 @@
+# Generated by Django 4.2.16 on 2024-11-08 13:36
+
+from django.db import migrations
+from django.db.models import F
+
+
+def remove_unnecessary_mails(apps, schema_editor):
+    ScheduledMail = apps.get_model("sendmail", "ScheduledMail")
+    ScheduledMail.objects.filter(rule__subevent__isnull=False).exclude(subevent=F('rule__subevent')).delete()
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("sendmail", "0007_bigint"),
+    ]
+
+    operations = [
+        migrations.RunPython(remove_unnecessary_mails),
+    ]

src/pretix/plugins/sendmail/signals.py

@@ -65,11 +65,10 @@ def scheduled_mail_create(sender, **kwargs):
     with scope(organizer=event.organizer):
         existing_rules = ScheduledMail.objects.filter(subevent=subevent).values_list('rule_id', flat=True)
         to_create = []
-        for rule in event.sendmail_rules.all():
-            if rule.pk not in existing_rules and subevent:
-                sm = ScheduledMail(rule=rule, event=event, subevent=subevent)
-                sm.recompute()
-                to_create.append(sm)
+        for rule in event.sendmail_rules.filter(subevent=None).exclude(id__in=existing_rules):
+            sm = ScheduledMail(rule=rule, event=event, subevent=subevent)
+            sm.recompute()
+            to_create.append(sm)
         ScheduledMail.objects.bulk_create(to_create)