[Django] #16995: ModelFormSet initial data from initial parameter uses "extra" forms
Django
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Reporter: p910221@… | Owner: nobody
Type: Bug | Status: new
Component: Forms | Version: 1.3
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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It seems that when you feed initial data into a ModelFromSet using the
initial parameter, it uses the "extra" forms that you define with the
extra parameter in the modelformset_factory. For example, if you feed a
list of two dictionaries (with the model data) into the initial parameter
of a FormSet, but the formset_factory that the FormSet was created from
has an extra parameter of 1 (or None), then only the model data from the
first dictionary in the list will show up in the FormSet.
Since "initial" data doen't seem like they should be in the "extra" forms,
I think this is a bug?
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Ticket URL: <https://code.djangoproject.com/ticket/16995>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
Type: Bug | Status: new
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Changes (by carljm):
* needs_better_patch: => 0
* component: Forms => Documentation
* needs_tests: => 0
* version: 1.3 => SVN
* needs_docs: => 0
* stage: Unreviewed => Accepted
Comment:
I believe this is working as designed. I do, however, think the
documentation is lacking in clarity and there's an inconsistency with how
`initial` works in a regular `FormSet`.
With a `FormSet`, `extra` forms are those beyond the ones created by the
data in `initial`, as
[https://docs.djangoproject.com/en/dev/topics/forms/formsets/#using-
initial-data-with-a-formset documented here].
With a `ModelFormSet`, the data in the non-extra forms is determined by
the existing model instances. It's sometimes useful to be able to pre-
populate some of the extra forms with some initial data, and that's what
the `initial` parameter is used for. If `initial` pre-populated the non-
extra forms, how would the conflict with existing model instance data be
resolved?
If this were being designed from scratch, you could perhaps make a case
that a `ModelFormSet` should consist of first the forms representing
existing instances, then forms representing the given `initial` data, then
empty `extra` forms (i.e. `initial` would add more forms, not prepopulate
the `extra` forms). This would perhaps be more consistent with `FormSet`,
but I'm not sure it's actually better for real usage.
In any case, if it's an improvement at all, it's not enough of one to
justify making a backwards-incompatible change. So I'm converting this
into a documentation bug; the `ModelFormSet`
[https://docs.djangoproject.com/en/dev/topics/forms/modelforms/#model-
formsets docs] should have an explanation of how `initial` and `extra`
interact differently in a `ModelFormSet` than in a `FormSet`.
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Ticket URL: <https://code.djangoproject.com/ticket/16995#comment:1>
Django
Type: Bug | Status: new
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
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>
Django
Reporter: p910221@… | Owner: nobody
Type: Bug | Status: new
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Comment (by alex.isayko@…):
The quick workaround on this is to use lambda function:
{{{
from django.forms.models import modelformset_factory
foos = some_function_that_returns_a_list_of_foo()
FooFormSet = lambda *args, **kwargs: modelformset_factory(Foo,
extra=kwargs.pop('extra', 0))(*args, **kwargs)
foo_formset = FooFormSet(initial=[f.__dict__ for f in foos],
extra=len(foos))
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/16995#comment:3>
Django
Reporter: p910221@… | Owner: S. Dole
| Melipone
Type: Bug | Status: assigned
Component: Documentation | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Changes (by S. Dole Melipone):
* owner: nobody => S. Dole Melipone
* status: new => assigned
Comment:
I will work on adding this to the documentation.
--
Ticket URL: <https://code.djangoproject.com/ticket/16995#comment:4>
Django
Reporter: p910221@… | Owner: S. Dole
| Melipone
Type: Bug | Status: assigned
Component: Documentation | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Changes (by S. Dole Melipone):
* has_patch: 0 => 1
Comment:
Patch and pull request created at
https://github.com/django/django/pull/10372
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Ticket URL: <https://code.djangoproject.com/ticket/16995#comment:5>
Django
Reporter: p910221@… | Owner: S. Dole
| Melipone
Type: Bug | Status: assigned
Component: Documentation | Version: master
Severity: Normal | Resolution:
| checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Changes (by Carlton Gibson):
* stage: Accepted => Ready for checkin
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Ticket URL: <https://code.djangoproject.com/ticket/16995#comment:6>
Django
Reporter: p910221@… | Owner: S. Dole
| Melipone
Component: Documentation | Version: master
Severity: Normal | Resolution: fixed
Keywords: | Triage Stage: Ready for
| checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Changes (by Tim Graham <timograham@…>):
* status: assigned => closed
* resolution: => fixed
Comment:
In [changeset:"28dac56aed1c8c9923b52a1ac3606996f9820b30" 28dac56a]:
{{{
#!CommitTicketReference repository=""
revision="28dac56aed1c8c9923b52a1ac3606996f9820b30"
Fixed #16995 -- Clarified interaction of initial and extra with model
formsets.
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/16995#comment:7>
Django
Reporter: p910221@… | Owner: S. Dole
| Melipone
Type: Bug | Status: closed
Component: Documentation | Version: master
Severity: Normal | Resolution: fixed
Keywords: | Triage Stage: Ready for
| checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Comment (by Tim Graham <timograham@…>):
In [changeset:"24b3aa0275717029f658906c6fbc2e8fec28949e" 24b3aa02]:
{{{
#!CommitTicketReference repository=""
revision="24b3aa0275717029f658906c6fbc2e8fec28949e"
[2.1.x] Fixed #16995 -- Clarified interaction of initial and extra with
model formsets.
Backport of 28dac56aed1c8c9923b52a1ac3606996f9820b30 from master
}}}
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Ticket URL: <https://code.djangoproject.com/ticket/16995#comment:8>