Filtering results based on the value of other fields in the form

Let’s say we want to add a “Continent” choice field in the form, and filter the countries based on the value on this field. We then need the widget to pass the value of the continent field to the view when it fetches data. We can use the forward widget argument to do this:

class PersonForm(forms.ModelForm):
    continent = forms.ChoiceField(choices=CONTINENT_CHOICES)

    class Meta:
        model = Person
        fields = ('__all__')
        widgets = {
            'birth_country': autocomplete.ModelSelect2(url='country-autocomplete'
                                                       forward=['continent'])
        }

This will pass the value for the “continent” form field in the AJAX request, and we can then filter as such in the view:

class CountryAutocomplete(autocomplete.Select2QuerySetView):
    def get_queryset(self):
        if not self.request.is_authenticated():
            return Country.objects.none()

        qs = Country.objects.all()

        continent = self.forwarded.get('continent', None)

        if continent:
            qs = qs.filter(continent=continent)

        if self.q:
            qs = qs.filter(name__istartswith=self.q)

        return self.q