django rest update_or_create - django

Question

Background:
I am trying to create a system which allows users to vote on comments written by other users (similar to Reddit). Users have the choice of three vote values: -1, 0, or 1. I have created a POST API (using django rest-framework) that will store a user's vote with respect to a particular comment. If the user has already voted on the given comment, then it will update the existing user’s vote value to the new one.
I drew inspiration from this post:Django RF update_or_create
Problem:
Once a comment has had one user submit a vote on it, Django creates a duplicate comment object with the same ID/primary key whenever another user votes on the same comment. I have taken a screenshot of my admin page where it says I have 3 objects to select but only a single comment. Why is it doing this and how can I prevent it?
Screenshot of my comment admin page
I am new to Django. I suspect I might be doing something wrong when I define my own "create" method in my serializer. I'd appreciate any help. Thanks!
models.py:
Comment model:
class Comment(models.Model):
location_property_category = models.ForeignKey('locations.LocationPropertyCategory',on_delete=models.CASCADE,related_name='comments',null=True)
author = models.ForeignKey('auth.User',on_delete=models.PROTECT,related_name='comments')
location = models.ForeignKey('locations.Location',on_delete=models.CASCADE,related_name='comments')
text = models.TextField()
create_date = models.DateTimeField(default=timezone.now())
published_date = models.DateTimeField(blank=True,null=True)
approved_comment = models.BooleanField(default=False)
objects = CommentManager()
def approve(self):
self.approved_comment = True
self.save()
def __str__(self):
return self.text
def save(self, *args, **kwargs):
if self.approved_comment is True:
self.published_date = timezone.now()
super(Comment, self).save(*args, **kwargs)
def sum_vote(self):
return self.upvotedownvotes.aggregate(Sum('vote')).get('vote__sum') or 0
Vote model:
class UpVoteDownVote(models.Model):
UPVOTE = 1
NEUTRALVOTE = 0
DOWNVOTE = -1
VOTES = (
(UPVOTE, 'Upvote'),
(NEUTRALVOTE, 'Neutralvote'),
(DOWNVOTE, 'Downvote')
)
vote = models.SmallIntegerField(choices=VOTES)
user = models.ForeignKey('auth.User', related_name='upvotedownvotes', on_delete=models.CASCADE)
comment = models.ForeignKey(Comment, related_name='upvotedownvotes', on_delete=models.CASCADE)
date_voted = models.DateTimeField(default=timezone.now())
class Meta:
unique_together = (('user','comment'),)
Comment manager model:
class CommentManager(models.Manager):
def get_queryset(self):
return super(CommentManager, self).get_queryset().order_by('-upvotedownvotes__vote')
serializers.py
Vote serializer:
class UpVoteDownVoteSerializer(serializers.ModelSerializer):
class Meta:
model = UpVoteDownVote
fields = ('vote','comment')
def get_fields(self):
fields = super(UpVoteDownVoteSerializer, self).get_fields()
fields['comment'].queryset = Comment.objects.filter(approved_comment=True)
return fields
def create(self, validated_data):
votedata, created = UpVoteDownVote.objects.update_or_create(
user=validated_data.get('user', None),
comment=validated_data.get('comment', None),
defaults={'vote': validated_data.get('vote', None),
})
return votedata
views.py
class UpVoteDownVoteCreateApiView(generics.CreateAPIView):
serializer_class = UpVoteDownVoteSerializer
permission_classes = [IsAuthenticated]
def perform_create(self,serializer):
serializer.save(user=self.request.user)
Comment app admin.py
class CommentAdmin(admin.ModelAdmin):
readonly_fields = ('id',)
admin.site.register(Comment,CommentAdmin)

Answer 1

Welcome to StackOverflow!
Your problem is in CommentManager:
queryset.order_by('-upvotedownvotes__vote')
This query basically creates LEFT_OUTER_JOIN. So you result looks like:
comment#1 upvote#1
comment#1 upvote#2
comment#1 upvote#3
That is why you are seeing comment#1 3 times.
I believe that you want to use something like this: https://docs.djangoproject.com/en/2.1/topics/db/aggregation/#order-by