Provide a hook for cross-form validation

oscar/apps/dashboard/catalogue/views.py

@@ -248,11 +248,12 @@ class ProductCreateUpdateView(generic.UpdateView):
         is_valid = form.is_valid() and all([formset.is_valid()
                                             for formset in formsets.values()])
 
-        if is_valid:
+        cross_form_validation_result = self.clean(form, formsets)
+        if is_valid and cross_form_validation_result:
             return self.forms_valid(form, formsets)
         else:
             # delete the temporary product again
-            if self.creating and form.is_valid():
+            if self.creating and self.object and self.object.pk is not None:
                 self.object.delete()
                 self.object = None
             return self.forms_invalid(form, formsets)
@@ -265,6 +266,15 @@ class ProductCreateUpdateView(generic.UpdateView):
     # redirect.
     form_valid = form_invalid = process_all_forms
 
+    def clean(self, form, formsets):
+        """
+        Perform any cross-form/formset validation. If there are errors, attach
+        errors to a form or a form field so that they are displayed to the user
+        and return False. If everything is valid, return True. This method will
+        be called regardless of whether the individual forms are valid.
+        """
+        return True
+
     def forms_valid(self, form, formsets):
         """
         Save all changes and display a success url.