http://chriskief.com/2013/10/29/advanced-django-class-based-views-modelforms-and-ajax-example-tutorial/

ajaxformresponse.py

from app.lib.shortcuts import render_to_json_response


# a mixin to add AJAX support to a form
# must be used with an object-based FormView (e.g. CreateView)
class AjaxFormResponseMixin(object):

    def form_invalid(self, form):
        return render_to_json_response(form.errors, status=400)

    def form_valid(self, form):

        # save
        self.object = form.save()

        # initialize an empty context
        context = {}

        # return the context as json
        return render_to_json_response(self.get_context_data(context))