#16995: ModelFormSet initial data from initial parameter uses "extra" forms
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Reporter: p910221@… | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: SVN
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by supervacuo):
I was about to report this as a separate bug (after asking in `#django-
dev`); I see this is as a feature proposal along the lines of "Set `extra`
to the length of `initial` in !ModelFormSet if it is not set manually".
I'm using `modelformset_factory` to create a model formset class, then
passing `initial` in the constructor when instantiating it. Line 91 of
`forms/formsets.py` uses the value of `extra` to work out how many `extra`
forms should be drawn, but I think this information could already be
implied by the length of the `initial` dict, at least in the case where
`extra` is not specified (for backwards compatibility), and having to
specify both seems a little like Repeating Yourself.
The code I'm using which demonstrates the problem is
[http://dpaste.org/QPWmn/ here].
I can certainly try writing a patch (it shouldn't be a big change, and I
imagine the tests would be pretty straightforward) if this seems like a
good idea. If not, I agree that the "Making forms from models" docs should
explain that `extra` needs to be set, even with `initial`, using something
like
{{{
from django.forms.models import modelformset_factory
foos = some_function_that_returns_a_list_of_foo()
FooFormSet = modelformset_factory(Foo, extra=len(foos))
foo_formset = FooFormSet(initial=[f.__dict__ for f in foos])
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/16995#comment:2>
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