#34711: form.has_changed() is always True for IntegerChoices Enum Model Field
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Reporter: GHPS | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 4.2
Severity: Normal | Keywords:
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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Summary:
While trying to find out why the forms in two different applications are
marked for saving even if no field has been changed, I could pin the
problem down
to the integer enum fields used in both models and form.ChoiceField
involved.
In short form.has_changed() is triggered because of a double data
conversion
during the round-trip.
The value of the integer enum field is converted to a string and rendered.
The POST request comes back with this string which gets compared to the
original
enum integer which shows that they are different. During the - unnecessary
- saving
the string becomes an int again - which is why the original problem is
hidden
from the perspective of a user.
Background:
In Django 4.2 on Linux (Kubuntu 22.04) take the following enum and
create a model field in model.py:
{{{
class eAssets(models.IntegerChoices):
dvd =1, _('DVD')
bluray =3, _('Blu-ray')
none =0, _('-')
eAsset=models.PositiveSmallIntegerField(choices=eAssets.choices,
default=eAssets.none)
}}}
Create a choice form field in form.py:
{{{
eAsset=forms.ChoiceField(label=mdMovie._meta.get_field('eAsset').verbose_name,
choices=[(dcEntry.value, dcEntry.label) for dcEntry in mdMovie.eAssets],
initial=mdMovie.eAssets.none)
After processing the POST request, form.has_changed() is always true in
view.py:
>fmForm=fmMovie(vRequest.POST, vRequest.FILES or None,
instance=rcCurrentMovie)
>fmForm.has_changed()
True
>fmForm.changed_data
['eAsset']
}}}
Links:
- I've found an old ticket #22097 and it looks to me like this nine year
old bug has shown its ugly face again.
- On Stackoverflow someone reported the same problem.
[https://stackoverflow.com/questions/68763230/django-forms-a-dynamic-
integer-model-choice-field-always-fails-form-has-changed|A dynamic integer
model choice field always fails form.has_changed()]
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Ticket URL: <https://code.djangoproject.com/ticket/34711>
Django <https://code.djangoproject.com/>
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