Add a form instantiation hook for contrib.admin add/change views

[tangc]

add_view and change_view have the following code:

ModelForm = self.get_form(request)
...
form = ModelForm(request.POST, request.FILES)

or:

 form = ModelForm(initial=initial)

or:

 form = ModelForm(request.POST, request.FILES, instance=obj)

I would propose:

if isinstance(ModelForm, ModelFormMetaclass):
    form = ModelForm(request.POST, request.FILES)
else
    form = ModelForm

This way gives the flexibility to override the function get_form(self, request, obj=None, **kwargs), which could return a modelform_factory(self.model, **defaults) or an instance of a model form.

[Alex Gaynor]

My inclination is that this is the wrong way to go about doing this, an "instiate_form" hook or somethign similar is a much better API design IMO.

[(none)]

Milestone post-1.0 deleted

[Tay Ray Chuan]

Changed the summary to be more informative.

[Julien Phalip]

Reformatted description to be more readable.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Jacob]

I agree with Alex: the proposed API is clumsy. But the need is real, so moving this to accepted. Determine a better API first though.

[Tim Graham]

#17577 is a duplicate.

[Romaric Pascal]

I've ran into the exact same need and thought it'd be great if ModelAdmin had that instanciate_form hook.

How does the following sound: The calls to ModelForm(...) inside ​_changeform_view could be replaced by self.get_form_instance(ModelForm, request, obj,...) which would pass any arguments to the ModelForm, but allow developers to intercept the call and maybe set initial values of their own based on the request or the current object.

Actually the get_form_instance default implementation could also be responsible for calling the get_form so that the signature doesn't require the form class to be passed (but that might be too many responsibilities for it and make things confusing).

Would be happy to contribute the change if that was fitting :D