#5126: Populate `initial_data` of forms from model instance
------------------------------------------------+---------------------------
Reporter: Christopher Lenz <[EMAIL PROTECTED]> | Owner:
adrian
Status: new | Component:
django.newforms
Version: SVN | Resolution:
Keywords: | Stage: Design
decision needed
Has_patch: 1 | Needs_docs: 0
Needs_tests: 1 | Needs_better_patch: 0
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Changes (by Christopher Lenz <[EMAIL PROTECTED]>):
* summary: Override constructor of `form_for_model` class to take model
instance => Populate `initial_data` of forms
from model instance
Comment:
Replying to [comment:1 SmileyChris]:
> I'm unconvinced on the merits of this ticket...
Then let me try a bit harder ;-)
Currently, if you don't use `form_for_instance`, there's simply no way in
the API to use a model instance to populate the initial data of the
form--short of workarounds such as the snippet you linked to. I think we
can agree that this is a pretty common thing to want to do with newforms,
and frankly, I'm puzzled by the omission.
If there's no argument about the ''why'', let's move to the ''how''. I see
three possible options to add this to the API, not necessarily mutually
exclusive:
1. A module-level function in `django.newforms.models` (see my second
patch):
{{{
#!python
form = MyForm()
forms.init_from_instance(form, myinstance)
}}}
This is the only option I can see for custom `Form` classes, unless you
want to add coupling between the regular forms code and the model-aware
forms stuff, or add an intermediary `ModelForm` subclass or something like
that.
2. An added regular instance method on the `Form` subclass produced by
`form_for_model()`
{{{
#!python
form = MyForm()
form.init(myinstance)
}}}
This is a bit nicer from an OO perspective.
2. Finally, an overridden constructor as initially proposed by this
ticket:
{{{
#!python
form = MyForm(myinstance)
}}}
(A variant of this last form would to accept the model instance as value
of the `initial` keyword argument.)
IMHO it's obvious which of those is the nicest, but I'd buy any of them.
To conclude, what I'd suggest is [attachment:ticket5126_2.diff] my second
patch, which adds the `init_from_instance` function for use with custom
`Form` classes, but still overrides the constructor
.
--
Ticket URL: <http://code.djangoproject.com/ticket/5126#comment:2>
Django Code <http://code.djangoproject.com/>
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