Andrzej Radzimiński added a comment - 2022-05-9 11:27 Reason: `adjust_preferences_factory_fields` adds field, that uses `user` to get default view. Then `RegistrationView` generates form using `PreferenceFactory` with `user` set to `None`. Possible fix: Lambda added in adjust_preferences_factory_fields can test is User is None. This fixes the problem, but `RegistrationView` now may or may not has preferences fields. Additionally preferences fields visible in registration form have will have no effect. To fix this `adjust_preferences_factory_fields`+`handle_new_preference_fields` logic should be added to `RegistrationView`. `Adjust_preferences_factory_fields` could be called once in same way `_maybe_add_field` is called, but I'm not sure if it will always work.

Tomek Waleń added a comment - 2022-05-4 16:08 Possible solution: diff --git a/oioioi/base/views.py b/oioioi/base/views.py index d5466e29..71819b6f 100644 --- a/oioioi/base/views.py +++ b/oioioi/base/views.py @@ -99,6 +99,8 @@ def adjust_preferences_factory_fields(request):      choices_not_translated = [("", "None")] + list(settings.LANGUAGES)      choices = [(k, _(v)) for k, v in choices_not_translated]   + ensure_preferences_exist_for_user(request) +      PreferencesFactory.add_field(          "preferred_language",          ChoiceField,