#29739: BaseModelFormSet ignores excess rows in initial when extra <
len(initial)
--------------------------------------------+------------------------------
Reporter: S. Dole Melipone | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 2.1
Severity: Normal | Keywords: modelformset
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
--------------------------------------------+------------------------------
When passing initial data through `BaseModelFormSet.__init__(...,
initial=)` and the length of the initial data exceeds the number of extra
forms defined in `modelformsetfactory(..., extra=)`, then the data in the
range `self.initial_extra[self.extra:]` will be ignored.
E.g.
{{{#!python
class Person(models.Model):
name = models.CharField(max_length=100)
initial = [{'name': 'Foo'}, {'name': 'Bar'}, {'name': 'Baz'}]
PersonFormSet = modelformsetfactory(Person, extra=2)
formset = MyModelFormSet(initial=initial)
}}}
Now, assuming that `models.Person.objects.all()` is empty,
{{{#!python
len(formset.forms) == 2
True
}}}
This is because `BaseFormSet.total_form_count()` blindly uses self.extra
and does not take into account the additional data in
`self.initial_extra`.
In order to work around this users would check `len(initial)` before
constructing the class and modify the `extra` kwarg to be
`max(len(initial), some_default_value)`. This causes issues when writing
abstract code which constructs the class separately from initialising it,
or reuses the same class with differing initial data. In these cases the
length of the initial data may not be known at the time of class
construction.
Possible solutions are the number of extra forms equals `self.extra +
len(self.initial_extra)` or `max(self.extra, len(self.initial_extra))`.
--
Ticket URL: <https://code.djangoproject.com/ticket/29739>
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