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

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