[Django] #37145: ModelFormSet breaks when changing prefix format

[Django]

#37145: ModelFormSet breaks when changing prefix format
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Reporter: JortRoelofs | Type: Bug
Status: new | Component: Forms
Version: 6.0 | Severity: Normal
Keywords: formset | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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I've been trying to change the way the widget prefixes are formatted to
make it work nicely with some JavaScript libraries. Here I ran into the
following bug.

{{{class BookForm(forms.ModelForm):}}}
{{{ class Meta:}}}
{{{ ...}}}

{{{ def add_prefix(self, field_name)}}}
{{{ # Here I use a period as separator instead of a dash.}}}
{{{ return f"{self.prefix}.{field_name}" if self.prefix else
field_name}}}

{{{BookFormSet = modelformset_factory(Book, form=BookForm)}}}


So far so good, this renders the way I expect it to. However, form
submission doesn't work, as the check for the primary key is hardcoded to
use a dash as separator
[https://github.com/django/django/blob/a2348c85fc6c20087935c74cd99340dd4ef2dcdc/django/forms/models.py#L739
here]. When looking for a primary key, it constructs a key with pk_key =
"%s-%s" % (self.add_prefix(i), self.model._meta.pk.name), but this is
inconsistent when the form itself has defined a different way to construct
prefixes.
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Ticket URL: <https://code.djangoproject.com/ticket/37145>
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