How to return JsonResponse in Django generic ListView

Question

I'm having trouble returning a valid HttpResponse in my ListView (and am getting a ValueError: The view didn't return an HttpResponse object... . I've overridden get because I want to return a JsonResponse:

def get(self, requets, *args, **kwargs):
    queryset = self.get_queryset()
    data = serializers.serialize("json", queryset)
    return JsonResponse(data, status=200, safe=False)

I've checked that queryset and data and the JsonResponse are not None . Changing the return statement doesn't work:

return HttpResponse(json.dumps(data), content_type="application/json", status=200)

Previously, if I ever needed to override get , I would return render(...) , which works.

So, why is my HttpResponse or JsonResponse not an acceptable HttpResponse as per the error in this instance? The GET request will be an ajax request, and I do need to provide some sensible json in reply.

Edit: full class

from django.core import serializers
from django.http import JsonResponse
@method_decorator(login_required, name='dispatch')
class AjaxQuestionList(ListView):
    """
    Generic ListView for Question objects. Called by front-end app.
    Requires hash url parameter to identify Survey.
    Intended to be called via ajax. Returns serialized json list of Questions.
    """
    http_method_names = ['get',]

    def dispatch(self, request, *args, **kwargs):
        #allow user to call this View if their Client owns the Survey
        self.survey = get_object_or_404(Survey, hash=self.kwargs['hash'])
        up = get_object_or_404(UserProfile, fk_user=self.request.user)
        self.client = up.fk_client
        if self.survey.fk_client != self.client:
            raise Http404
        super(AjaxQuestionList, self).dispatch(request, *args, **kwargs)

    def get_queryset(self):
        return Question.objects.filter(fk_survey=self.survey)

    def get(self, request, *args, **kwargs):
        queryset = self.get_queryset()
        data = serializers.serialize("json", queryset)
        return JsonResponse(data, status=200, safe=False)

Traceback:

File "/webapps/escher/lib/python3.5/site-packages/django/core/handlers/exception.py" in inner 39. response = get_response(request)

File "/webapps/escher/lib/python3.5/site-packages/django/core/handlers/base.py" in _legacy_get_response 249. response = self._get_response(request)

File "/webapps/escher/lib/python3.5/site-packages/django/core/handlers/base.py" in _get_response 198. "returned None instead." % (callback. module , view_name)

Exception Type: ValueError at /si/survey/123456789/ajax-question-list/ Exception Value: The view myapp.views.survey.AjaxQuestionList didn't return an HttpResponse object. It returned None instead.

From the CBV flattened index I just assumed that render_to_response() was called automatically after get() , rendering whatever HttpResponse get() returned. Am I mistaken?

Answer 1

You need to return the result of super() in your dispatch method.

def dispatch(self, request, *args, **kwargs):
    ... 
    return super(AjaxQuestionList, self).dispatch(request, *args, **kwargs)

Without the return statement, the method returns None so you get the error message.