full_clean() called too many times during formset validation

[Claude Paroz]

I have a formset with 3 forms in it. I had to debug some stuff with it, but then I realized the full_clean method is called 21 times when calling the formset.is_valid(), while I would expect 4 times (once for the formset itself and once for each subform). For example, a validation occurs each time the management_form property is called. While it may not cause real issues in practice, it's poor design and annoying when trying to debug and follow the validation workflow.

[Tim Graham]

I think I'm lacking some details to understand this. Is this for plain formsets and/or model formsets? Are the duplicated calls to BaseFormSet.full_clean() and/or some other full_clean()? For example, I added some debugging in Django's test_basic_formset but only saw BaseFormSet.full_clean() called once.

[Claude Paroz]

I think this affects all sort of formsets. The problem might rather affect the full_clean() methods of included subforms (notably for the management form).

[Tim Graham]

Making BaseFormSet.management_form a @cached_property seems to help (not sure if it fully resolves the issue).

[Karol Sztajerwald]

PR here: ​https://github.com/django/django/pull/7496

[Claude Paroz]

Tests added in that ​PR.

[GitHub <noreply@…>]

In d49551bc:

Fixed #27119 -- Cached BaseFormSet.management_form property

Thanks Tim Graham for the review.