#18508: Bug in handling out-of-date POST data with inlineformset_factory
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Reporter: olau | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 1.4
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Hi, there's a bug in BaseModelFormSet._construct_form. There's a guard
supposed to take care of bound forms, but if one of the entries has been
deleted, self._existing_object(pk) will return None so you can end up in
{{{
if i < self.initial_form_count() and not kwargs.get('instance'):
kwargs['instance'] = self.get_queryset()[i]
}}}
which is dangerous for a bound form where you must use ids to identify
elements since element "i" can have changed from when the form was
generated. In my case, I got an IndexError because there weren't enough
elements left from a recent deletion.
I think the correct fix is to change the "if" to an "elif".
I've attached a patch with this fix and a test case for reproducing the
problem (there doesn't seem to be any tests of model formsets?).
Note that the test as entered doesn't pass even with the fix because of
issue #14877 - if you delete formset.save() and below in the test, it does
pass.
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Ticket URL: <https://code.djangoproject.com/ticket/18508>
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