Check if user voted and if not save vote - django

Question

In a simple survey app users should vote only once on a set of questions (survey). I'm able to check if the user voted (either lazy user or authorized user), but only if I prepopulate the fields with test data in the database. I'm also aware that a lazy user could just delete the cookie and would be able to vote again.
I'm not sure how to call save() after form.is_valid(), because I can't call it twice.
models.py
class Vote(models.Model):
user = models.ForeignKey(User)
survey = models.ForeignKey(Survey)
vote = models.BooleanField(default=False) # not in use yet
def __unicode__(self):
return self.vote
views.py
#allow_lazy_user
def survey_detail(request, slug, template_name='survey.html'):
# allows only active surveys to be called otherwise displays HTTP 404
survey = get_object_or_404(Survey, is_active=True, slug=slug)
# checks for user id's in current survey
voter = [
v.user.id for v in Vote.objects.filter(survey=survey)
]
# checks if user already voted on survey
if request.user.id in voter:
# TODO: use different template or redirect
return render(request, 'index.html')
form = ResponseForm(request.POST or None, survey=survey)
if form.is_valid():
response = form.save(commit=False)
# gets the current user (lazy or not)
response.user = request.user
response.save()
# HOW DO I SAVE VOTER HERE?
return HttpResponseRedirect(reverse('survey:confirm', args=(slug,)))
data = {
'response_form': form,
'survey': survey
}
return render(request, template_name, data)
Another thought I have is to use the boolean field vote in the model and check for True or False in the template.

Answer 1

Okay, I solved it with
#allow_lazy_user
def survey_detail(request, slug, template_name='survey.html'):
[...]
form = ResponseForm(request.POST or None, survey=survey)
if form.is_valid():
response = form.save(commit=False)
response.user = request.user
response.save()
if not request.user.id in voter:
vote = Vote(user=request.user, survey=survey, vote=True)
vote.save()
return HttpResponseRedirect(reverse('survey:confirm', args=(slug,)))
[...]
I'm sure there are better ways, but it works for now.

Answer 2

New solution, since survey_id and user_id are already in model Response:
#allow_lazy_user
def survey_detail(request, slug, template_name='itbarometer/survey_detail.html'):
# allows only active surveys to be called otherwise displays HTTP 404
survey = get_object_or_404(Survey, is_active=True, slug=slug)
categories = [c.name for c in Category.objects.filter(survey=survey)]
voter = [v.user.id for v in Response.objects.filter(survey=survey)]
# checks if survey_id and user_id are already linked
# if yes, redirect
if request.user.id in voter:
return redirect('bereits-abgeschlossen/')
form = ResponseForm(request.POST or None, survey=survey)
if form.is_valid():
response = form.save(commit=False)
# gets the current user (lazy or not)
response.user = request.user
response.save()
return HttpResponseRedirect(reverse('survey:confirm', args=(slug,)))
data = {
'response_form': form,
'survey': survey,
'categories': categories
}
return render(request, template_name, data)