Django Passing Custom Form Parameters to Formset

Paolo_Bergantino_16417 0
Viewed 49264

This was fixed in Django 1.9 with form_kwargs.

I have a Django Form that looks like this:

class ServiceForm(forms.Form):
    option = forms.ModelChoiceField(queryset=ServiceOption.objects.none())
    rate = forms.DecimalField(widget=custom_widgets.SmallField())
    units = forms.IntegerField(min_value=1, widget=custom_widgets.SmallField())

    def __init__(self, *args, **kwargs):
        affiliate = kwargs.pop('affiliate')
        super(ServiceForm, self).__init__(*args, **kwargs)
        self.fields["option"].queryset = ServiceOption.objects.filter(affiliate=affiliate)

I call this form with something like this:

form = ServiceForm(affiliate=request.affiliate)

Where request.affiliate is the logged in user. This works as intended.

My problem is that I now want to turn this single form into a formset. What I can't figure out is how I can pass the affiliate information to the individual forms when creating the formset. According to the docs to make a formset out of this I need to do something like this:

ServiceFormSet = forms.formsets.formset_factory(ServiceForm, extra=3)

And then I need to create it like this:

formset = ServiceFormSet()

Now how can I pass affiliate=request.affiliate to the individual forms this way?

forms django-forms django python
12 Answers

I would use functools.partial and functools.wraps:

from functools import partial, wraps
from django.forms.formsets import formset_factory

ServiceFormSet = formset_factory(wraps(ServiceForm)(partial(ServiceForm, affiliate=request.affiliate)), extra=3)

I think this is the cleanest approach, and doesn't affect ServiceForm in any way (i.e. by making it difficult to subclass).

Carl_Meyer_32070

I would build the form class dynamically in a function, so that it has access to the affiliate via closure:

def make_service_form(affiliate):
    class ServiceForm(forms.Form):
        option = forms.ModelChoiceField(
                queryset=ServiceOption.objects.filter(affiliate=affiliate))
        rate = forms.DecimalField(widget=custom_widgets.SmallField())
        units = forms.IntegerField(min_value=1, 
                widget=custom_widgets.SmallField())
    return ServiceForm

As a bonus, you don't have to rewrite the queryset in the option field. The downside is that subclassing is a little funky. (Any subclass has to be made in a similar way.)

edit:

In response to a comment, you can call this function about any place you would use the class name:

def view(request):
    affiliate = get_object_or_404(id=request.GET.get('id'))
    formset_cls = formset_factory(make_service_form(affiliate))
    formset = formset_cls(request.POST)
    ...
mmarshall_398560

I like the closure solution for being "cleaner" and more Pythonic (so +1 to mmarshall answer) but Django forms also have a callback mechanism you can use for filtering querysets in formsets.

It's also not documented, which I think is an indicator the Django devs might not like it as much.

So you basically create your formset the same but add the callback:

ServiceFormSet = forms.formsets.formset_factory(
    ServiceForm, extra=3, formfield_callback=Callback('option', affiliate).cb)

This is creating an instance of a class that looks like this:

class Callback(object):
    def __init__(self, field_name, aff):
        self._field_name = field_name
        self._aff = aff
    def cb(self, field, **kwargs):
        nf = field.formfield(**kwargs)
        if field.name == self._field_name:  # this is 'options' field
            nf.queryset = ServiceOption.objects.filter(affiliate=self._aff)
        return nf

This should give you the general idea. It's a little more complex making the callback an object method like this, but gives you a little more flexibility as opposed to doing a simple function callback.

Van_Gale_342580

I wanted to place this as a comment to Carl Meyers answer, but since that requires points I just placed it here. This took me 2 hours to figure out so I hope it will help someone.

A note about using the inlineformset_factory.

I used that solution my self and it worked perfect, until I tried it with the inlineformset_factory. I was running Django 1.0.2 and got some strange KeyError exception. I upgraded to latest trunk and it worked direct.

I can now use it similar to this:

BookFormSet = inlineformset_factory(Author, Book, form=BookForm)
BookFormSet.form = staticmethod(curry(BookForm, user=request.user))
user_317850
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