Fix form validation of exporters (again)

src/pretix/control/views/organizer.py

@@ -1147,8 +1147,9 @@ class ExportMixin:
             organizer=self.request.organizer
         )
         responses = register_multievent_data_exporters.send(self.request.organizer)
+        id = self.request.GET.get("identifier") or self.request.POST.get("exporter")
         for ex in sorted([response(events) for r, response in responses if response], key=lambda ex: str(ex.verbose_name)):
-            if self.request.GET.get("identifier") and ex.identifier != self.request.GET.get("identifier"):
+            if id and ex.identifier != id:
                 continue
 
             # Use form parse cycle to generate useful defaults
@@ -1180,10 +1181,16 @@ class ExportMixin:
             exporters.append(ex)
         return exporters
 
+    def get_context_data(self, **kwargs):
+        ctx = super().get_context_data(**kwargs)
+        ctx['exporters'] = self.exporters
+        return ctx
 
-class ExportDoView(OrganizerPermissionRequiredMixin, ExportMixin, AsyncAction, View):
+
+class ExportDoView(OrganizerPermissionRequiredMixin, ExportMixin, AsyncAction, TemplateView):
     known_errortypes = ['ExportError']
     task = multiexport
+    template_name = 'pretixcontrol/organizers/export.html'
 
     def get_success_message(self, value):
         return None
@@ -1202,6 +1209,11 @@ class ExportDoView(OrganizerPermissionRequiredMixin, ExportMixin, AsyncAction, V
             if ex.identifier == self.request.POST.get("exporter"):
                 return ex
 
+    def get(self, request, *args, **kwargs):
+        if 'async_id' in request.GET and settings.HAS_CELERY:
+            return self.get_result(request)
+        return TemplateView.get(self, request, *args, **kwargs)
+
     def post(self, request, *args, **kwargs):
         if not self.exporter:
             messages.error(self.request, _('The selected exporter was not found.'))
@@ -1231,11 +1243,6 @@ class ExportDoView(OrganizerPermissionRequiredMixin, ExportMixin, AsyncAction, V
 class ExportView(OrganizerPermissionRequiredMixin, ExportMixin, TemplateView):
     template_name = 'pretixcontrol/organizers/export.html'
 
-    def get_context_data(self, **kwargs):
-        ctx = super().get_context_data(**kwargs)
-        ctx['exporters'] = self.exporters
-        return ctx
-
 
 class GateListView(OrganizerDetailViewMixin, OrganizerPermissionRequiredMixin, ListView):
     model = Gate