How Can I Restrict One Vote For One User?

Question

My models.py is this and I have created the user registration form. I want to restrict one vote for one user. How Can I do so?

class Choice(models.Model):
    choice_text = models.CharField(max_length= 200)
    votes = models.IntegerField(default= 0)
    image2 = models.ImageField(upload_to="Question_Image2", blank=True)
    question = models.ForeignKey(Question, on_delete= models.CASCADE)

    def __str__(self):
        return  self.choice_text

    def vote_range(self):
        return range(0, self.votes)

My views.py is this for vote

def vote(request, question_id):
    question = get_object_or_404(Question, pk= question_id)
    try:
        selected_choice = question.choice_set.get(pk = request.POST['choice'])
    except:
        return render(request, 'polls/detail.html', {'question':question, 'error_message':"Please select a choice"})
    else:
        selected_choice.votes += 1
        selected_choice.save()

        return HttpResponseRedirect(reverse('polls:results',args = (question.id,)))

Answer 1

You should add a Vote model

class Vote(models.Model):
    date_added = models.DateTimeField(auto_now_add=True)
    user = models.ForeignKey(User, unique=True)
    choice = models.ForeignKey(Choice)

But i think maybe a more complete idea would be

class Vote(models.Model):
    date_added = models.DateTimeField(auto_now_add=True)
    user = models.ForeignKey(User
    choice = models.ForeignKey(Choice)
    election = models.ForeignKey(Election)

    class Meta:
        unique_together = ('user', 'election')