Question

我希望用户只能对类别请求进行一次投票，但是不知何故我收到了以下错误，并且我不知道该如何“正确地”调用实例：

无法分配“ 1”：“ CategoryRequests_Voter.voted”必须为 “ CategoryRequests”实例。

models.py

# Category Requests Model
class CategoryRequests(models.Model):
    author = models.ForeignKey(User, on_delete=models.CASCADE)

    ....

# Vote(s) of Category Requests Model
class CategoryRequests_Voter(models.Model):
    voter = models.ForeignKey(User, on_delete=models.CASCADE)
    voted = models.ForeignKey(CategoryRequests, on_delete=models.CASCADE)
    published_date = models.DateField(auto_now_add=True, null=True)

    def publish(self):
        self.published_date = timezone.now()
        self.save()

views.py

def category_request_up_vote (request, pk):
    category_request = get_object_or_404(CategoryRequests, pk=pk)
    if request.method == 'GET':
        if CategoryRequests_Voter.objects.filter(voter=request.user, voted=category_request.pk).exists():
            messages.error(request, 'You already voted for this request.')
        else:
            category_request.up_vote = F('up_vote') + 1
            category_request.save()
            CategoryRequests_Voter.objects.create(voter=request.user, voted=category_request.pk)
            messages.success(request, 'You have successfully Provided an Up-Vote for this Request')
            return redirect('category_request_detail', pk=category_request.pk)
    else:
        messages.error(request, 'Uuups, something went wrong, please try again.')
        return redirect('category_request_detail', pk=category_request.pk)

预先感谢

Answer 1

您需要将voted参数固定为category_request，而不是其主键，例如：

CategoryRequests_Voter.objects.create(voter=request.user, voted=category_request)

但是，您可以改进模型和视图以提高一致性和美观性。为了防止User进行两次或两次以上的投票，可以防止为相同 CategoryRequest_Voter和voter创建两次创建voted对象的过程，通过使用unique_together约束：

class CategoryRequests_Voter(models.Model):
    voter = models.ForeignKey(User, on_delete=models.CASCADE)
    voted = models.ForeignKey(CategoryRequests, on_delete=models.CASCADE)
    published_date = models.DateField(auto_now_add=True, null=True)

    class Meta:
        unique_together = ('voter', 'voted')

    def publish(self):
        self.published_date = timezone.now()
        self.save()

此外，我们可以使用get_or_create并因此仅从数据库中进行一次读取。通常，更改数据的视图应使用POST请求（而不是GET）来执行此操作。 GET请求不应有副作用。

def category_request_up_vote (request, pk):
    category_request = get_object_or_404(CategoryRequests, pk=pk)
    if request.method == 'POST':
        __, created = CategoryRequests_Voter.objects.get_or_create(
            voter=request.user,
            voted=category_request
        )
        if created:
            category_request.up_vote = F('up_vote') + 1
            category_request.save()
            messages.success(request, 'You have successfully Provided an Up-Vote for this Request')
        else:
            messages.error(request, 'You already voted for this request.')
    else:
        messages.error(request, 'Uuups, something went wrong, please try again.')
    return redirect('category_request_detail', pk=category_request.pk)

也许值得计算CategoryRequest_Voter的数量，而不是增加投票数，因为例如由于删除User或票数，最终可能会投票数不再与该CategoryRequests_Voter对象的CategoryRequests数一致。

也许计数对象的数量并不是有效的每次投票，但是您可以使任务不时地运行，从而计算：

CategoryRequests_Voter.objects.filter(voted=category_request).count()

计算给定CategoryRequests_Voter的{{1}}的数量。

Answer 2

def category_request_up_vote (request, pk):
    category_request = get_object_or_404(CategoryRequests, pk=pk)
    try:
        if request.method == 'GET':
            if CategoryRequests_Voter.objects.filter(voter=request.user, voted=category_request).exists():
                messages.error(request, 'You already voted for this request.')
                return redirect('category_request_detail', pk=category_request.pk)
            else:
                category_request.up_vote = F('up_vote') + 1
                category_request.save()
                CategoryRequests_Voter.objects.create(voter=request.user, voted=category_request)
                messages.success(request, 'You have successfully Provided an Up-Vote for this Request')
                return redirect('category_request_detail', pk=category_request.pk)
        else:
            messages.error(request, 'Uuups, something went wrong, please try again.')
            return redirect('category_request_detail', pk=category_request.pk)
    except:
        messages.error(request, 'Uuups, something went wrong, please try again.')
        return redirect('category_request_detail', pk=category_request.pk)

Django-用户只能投票一次

2 个答案: