django-addanother with django-autocomplete-light and GenericForeignKeys

admin.py

# Source: https://github.com/yourlabs/django-autocomplete-light/blob/master/test_project/select2_generic_foreign_key/admin.py

import json

from django.contrib import admin
from django.contrib.admin.options import IS_POPUP_VAR, TO_FIELD_VAR
from django.contrib.contenttypes.models import ContentType
from django.template.response import TemplateResponse

from .forms import TForm
from .models import TModel


class TestAdmin(admin.ModelAdmin):
    form = TForm

    # Source: https://github.com/django/django/blob/fed8129276eac973fd48a2f33b7e1735a866628d/django/contrib/admin/options.py#L1175
    # Extend response_add to customise popup handling.
    def response_add(self, request, obj, post_url_continue=None):
        if IS_POPUP_VAR not in request.POST:
            return super().response_add(request, obj, post_url_continue)
        else:
            """
            Determine the HttpResponse for the add_view stage.
            """
            opts = obj._meta

            to_field = request.POST.get(TO_FIELD_VAR)
            if to_field:
                attr = str(to_field)
            else:
                attr = obj._meta.pk.attname
            value = obj.serializable_value(attr)
            ctype = ContentType.objects.get_for_model(obj)
            popup_response_data = json.dumps({
                # KEY LINE: Ensure ctype is returned as part of the value
                'value': '%s-%s' % (ctype.id, value),
                'obj': str(obj),
            })
            return TemplateResponse(request, self.popup_response_template or [
                'admin/%s/%s/popup_response.html' % (opts.app_label, opts.model_name),
                'admin/%s/popup_response.html' % opts.app_label,
                'admin/popup_response.html',
            ], {
                'popup_response_data': popup_response_data,
            })

admin.site.register(TModel, TestAdmin)

forms.py

from dal import autocomplete

from dal_select2_queryset_sequence.views import Select2QuerySetSequenceView
from dal_select2_queryset_sequence.widgets import QuerySetSequenceSelect2

from django.contrib.auth.models import Group

from .models import TModel
from .widgets import AddAnotherWidgetWrapper


class TForm(autocomplete.FutureModelForm):
    # Either of these ModelFields work fine.

    test = autocomplete.Select2GenericForeignKeyModelField(
        model_choice=[
            (Group, 'name'),
            (TModel, 'name', [('name', 'name')])
        ],  # Model with values to filter

        required=False,
        field_id='test',
    )

    test2 = autocomplete.GenericForeignKeyModelField(
        model_choice=[(Group,), (TModel,)],
        required=False,
        widget=QuerySetSequenceSelect2,
        view=Select2QuerySetSequenceView,
    )
    
    # ADD THIS
    # Note: Only tested for admin forms.
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.fields['test'].widget = (
            AddAnotherWidgetWrapper(
                self.fields['test'].widget,
                reverse_lazy('[THE ADMIN ADD LINK]')
            )
        )

    class Meta:
        model = TModel
        fields = ('name',)

widgets.py

from django_addanother.widgets import AddAnotherWidgetWrapper as AddAnother


class AddAnotherWidgetWrapper(AddAnother):
    def __init__(self, widget, add_related_url, add_icon=None):
        # ADD THIS: Need to set self.choices or it will error
        self.choices = widget.choices
        super().__init__(
            widget, add_related_url, add_icon
        )