python - 投票正在添加多票

Question

我正在构建一个 PollApp，但我遇到了一个问题。
我想做什么:-
我只想在 One choice at a time 上投票如果用户想更改 voting choice然后用户也可以更改选择。但是此时，当用户选择 first choice 时那么它会一次又一次地添加投票，如果用户选择 second option然后两者都在添加(第一选择和第二选择)。但我试图一次只添加一个选择。
View .py

def poll_vote(request, poll_id):
    poll = get_object_or_404(Poll, pk=poll_id)
    choice_id = request.POST.get('choice')

    if choice_id:
        choice = Choice.objects.get(id=choice_id)
        vote = Vote(user=request.user, poll=poll, choice=choice)
        vote.save()
        print(vote)
        return render(request, 'polls/poll_result.html', {'poll': poll})
    else:
        messages.error(
            request, "No choice selected")
        return redirect("polls:polls_detail_view", poll_id)
    return render(request, 'polls/poll_result.html', {'poll': poll})

我也在 poll_vote 中尝试过这个看法

    if not poll.user_can_vote(request.user):
        messages.error(request, "You already voted this poll")
        return redirect("polls:polls_detail_view",poll_id=poll_id)

这工作正常，例如:- 当用户投票时 first choice然后它阻止用户选择第二个选项但我想要，用户可以在投票后更改另一个选项。
模型.py

class Poll(models.Model):
    owner = models.ForeignKey(User,null=True,on_delete=models.CASCADE)
    text = models.TextField()
    date = models.DateTimeField(default=timezone.now)

    def user_can_vote(self, user):

        user_votes = user.vote_set.all()
        qs = user_votes.filter(poll=self)
        if qs.exists():
            return False
        return True

class Choice(models.Model):
    poll = models.ForeignKey(Poll,on_delete=models.CASCADE)
    choice_text = models.CharField(max_length=30)


class Vote(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    poll = models.ForeignKey(Poll,on_delete=models.CASCADE)
    choice = models.ForeignKey(Choice,on_delete=models.CASCADE)

我不知道，如何让用户在投票后更改投票选择。
任何帮助将非常感激。
先感谢您。

Answer 1

您可以使用 update_or_create [Django docs]更新现有投票或创建新投票:

def poll_vote(request, poll_id):
    poll = get_object_or_404(Poll, pk=poll_id)
    choice_id = request.POST.get('choice')

    if choice_id:
        choice = Choice.objects.get(id=choice_id)
        vote, created = Vote.objects.update_or_create(
            user=request.user,
            poll=poll,
            defaults={'choice': choice}
        )
        print(vote)
        return render(request, 'polls/poll_result.html', {'poll': poll})
    else:
        messages.error(
            request, "No choice selected")
        return redirect("polls:polls_detail_view", poll_id)
    return render(request, 'polls/poll_result.html', {'poll': poll})

如果您有 Vote 的任何重复实例你应该在使用它之前先删除它们。你也应该添加一个 UniqueConstraint [Django docs]给您的 Vote防止重复的模型:

class Vote(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    poll = models.ForeignKey(Poll,on_delete=models.CASCADE)
    choice = models.ForeignKey(Choice,on_delete=models.CASCADE)
    
    class Meta:
        constraints = [
            models.UniqueConstraint(fields=['user', 'poll'], name='unique_user_poll')
        ]