Solve cart deletion issues once and for all

src/pretix/api/views/event.py

@@ -272,6 +272,8 @@ class SubEventViewSet(ConditionalListView, viewsets.ModelViewSet):
                     auth=self.request.auth,
                     data=self.request.data
                 )
+                instance.cartposition_set.filter(addon_to__isnull=False).delete()
+                instance.cartposition_set.all().delete()
                 super().perform_destroy(instance)
         except ProtectedError:
             raise PermissionDenied('The sub-event could not be deleted as some constraints (e.g. data created by '

src/pretix/api/views/item.py

@@ -84,6 +84,7 @@ class ItemViewSet(ConditionalListView, viewsets.ModelViewSet):
             user=self.request.user,
             auth=self.request.auth,
         )
+        self.get_object().cartposition_set.filter(addon_to__isnull=False).delete()
         self.get_object().cartposition_set.all().delete()
         super().perform_destroy(instance)
 

src/pretix/api/views/voucher.py

@@ -111,7 +111,10 @@ class VoucherViewSet(viewsets.ModelViewSet):
             user=self.request.user,
             auth=self.request.auth,
         )
-        super().perform_destroy(instance)
+        with transaction.atomic():
+            instance.cartposition_set.filter(addon_to__isnull=False).delete()
+            instance.cartposition_set.all().delete()
+            super().perform_destroy(instance)
 
     @list_route(methods=['POST'])
     def batch_create(self, request, *args, **kwargs):