How to dynamically set the queryset of a models.ModelChoiceField on a forms.Form subclass

The constructor 开发者_如何学运维for forms.ModelChoiceField requires a queryset. I do not know the queryset until the request happens. Distilled:

# models.py
class Bar(models.model):
    text = models.TextField()

class Foo(models.Model):
    name = models.CharField()
    bar = models.ForeignKey(Bar)

# forms.py
class FooForm(forms.Form):
    name = forms.CharField()
    text = forms.CharField(widget=forms.TextArea)

    bar = forms.ModelChoiceField(queryset='??????')

What I am currently doing:

# forms.py

def get_foo_form_class(bars_queryset):
    class FooForm(forms.Form):
        name = forms.CharField()
        text = forms.CharField(widget=forms.TextArea)

        bar = forms.ModelChoiceField(queryset=bars_queryset)

    return FooForm

I can then call it in the view using arguments parsed out of the url with a urlconf to construct the queryset and get the class. This feels like the wrong way to do it. Is there an established way to do this in django?

Override the form's __init__ method and set the queryset there.

class FooForm(forms.Form):
    bar = forms.ModelChoiceField(queryset=Bar.objects.none())

    def __init__(self, *args, **kwargs):
        qs = kwargs.pop('bars')
        super(FooForm, self).__init__(*args, **kwargs)
        self.fields['bar'].queryset = qs

You can also do it in your view before you present the form in the template. I use this and find it more flexible incase you re-use the form in other views and need to change the queryset each time:

from assets.models import Asset
location_id = '123456'
edit_form = AsssetSelectForm(request.POST or None, instance=selected_asset)
edit_form.fields["asset"].queryset = Asset.objects.filter(location_id=location_id)

I also set the default queryset to none in the forms.py:

class AsssetSelectForm(forms.Form):
    asset = forms.ModelChoiceField(queryset=Asset.objects.none())