[英]Django - User should only able to vote once
我希望用户只能为类别请求投票一次,但不知何故我收到以下错误,我不知道此时如何“正确”调用实例:
无法分配“1”:“CategoryRequests_Voter.voted”必须是“CategoryRequests”实例。
模型.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()
视图.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)
提前致谢
您需要将voted
参数修复为仅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优雅度。 为了防止User
投票两次或更多次,您可以通过使用unique_together
约束来防止为同一个voter
创建两次CategoryRequest_Voter
对象并voted
:
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
从而只从数据库中进行一次提取。 通常,更改数据的视图应该使用 POST 请求而不是 GET 来执行此操作。 GET 请求不应该有副作用。
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)
可能值得计算CategoryRequest_Voter
的数量,而不是增加投票计数,因为有可能,例如由于删除User
或投票,最终投票数量不再与数量一致的CategoryRequests_Voter
■对于CategoryRequests
对象。
也许每次投票计算对象的数量并不是那么有效,但是您可以创建一个不时运行的任务,从而计算:
CategoryRequests_Voter.objects.filter(voted=category_request).count()
计算给定category_request
的CategoryRequests_Voter
的数量。
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)
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