Filter question by sales channel, default to pretixpos for POS devices

src/pretix/api/views/item.py

@@ -467,7 +467,6 @@ with scopes_disabled():
     class CompatQuestionFilter(FilterSet):
         identifier = django_filters.CharFilter(field_name='question__identifier')
         ask_during_checkin = django_filters.BooleanFilter(method='ask_during_checkin_qs')
-        sales_channel = django_filters.CharFilter(method='sales_channel_qs')
 
         class Meta:
             model = QuestionnaireChild
@@ -478,11 +477,6 @@ with scopes_disabled():
                 questionnaire__type=Questionnaire.QuestionnaireType.ORDER_POSITION_CHECKIN if value else Questionnaire.QuestionnaireType.ORDER_POSITION_SALE
             )
 
-        def sales_channel_qs(self, qs, name, value):
-            return qs.filter(
-                Q(questionnaire__all_sales_channels=True) | Q(questionnaire__limit_sales_channels__identifier=value)
-            )
-
 
 class CompatQuestionViewSet(ConditionalListView, viewsets.ModelViewSet):
     serializer_class = CompatQuestionSerializer
@@ -495,7 +489,9 @@ class CompatQuestionViewSet(ConditionalListView, viewsets.ModelViewSet):
     write_permission = 'event.items:write'
 
     def get_queryset(self):
+        self.sales_channel_ident = self.request.query_params.get('sales_channel', getattr(self.request.auth, 'guessed_sales_channel_identifier', None) or 'web')
         return QuestionnaireChild.objects.filter(
+            Q(questionnaire__all_sales_channels=True) | Q(questionnaire__limit_sales_channels__identifier=self.sales_channel_ident),
             questionnaire__event=self.request.event,
             # legacy compat only for position-level questions
             questionnaire__type__startswith='P',

src/pretix/base/models/devices.py

@@ -292,6 +292,11 @@ class Device(LoggedModel):
         else:
             return self.organizer.events.none()
 
+    @property
+    def guessed_sales_channel_identifier(self):
+        if self.software_brand.startswith("pretixPOS"):
+            return 'pretixpos'
+
 
 class DeviceLastSeen(models.Model):
     # This is a separate model since we expect it to get A LOT of writes and PostgreSQL always