Prepare for DeleteView change in Django 4.0

src/pretix/helpers/compat.py

@@ -22,9 +22,39 @@
 import datetime
 import sys
 
+from django.forms import Form
+from django.views.generic.detail import (
+    BaseDetailView, SingleObjectTemplateResponseMixin,
+)
+from django.views.generic.edit import DeletionMixin, FormMixin
+
 
 def date_fromisocalendar(isoyear, isoweek, isoday):
     if sys.version_info < (3, 8):
         return datetime.datetime.strptime(f'{isoyear}-W{isoweek}-{isoday}', "%G-W%V-%u")
     else:
         return datetime.datetime.fromisocalendar(isoyear, isoweek, isoday)
+
+
+class CompatDeleteView(SingleObjectTemplateResponseMixin, DeletionMixin, FormMixin, BaseDetailView):
+    """
+    This is a DeleteView variant that allows us to create subclasses that work on both Django 3.2 and
+    Django 4.0.
+    """
+    form_class = Form
+    template_name_suffix = "_confirm_delete"
+
+    def post(self, request, *args, **kwargs):
+        # Set self.object before the usual form processing flow.
+        # Inlined because having DeletionMixin as the first base, for
+        # get_success_url(), makes leveraging super() with ProcessFormView
+        # overly complex.
+        self.object = self.get_object()
+        form = self.get_form()
+        if form.is_valid():
+            return self.form_valid(form)
+        else:
+            return self.form_invalid(form)
+
+    def form_valid(self, form):
+        return self.delete(self.request, self.args, self.kwargs)