DRF | Django | Up votes | Down Votes

[DJANGO DEVELOPER]

Hi Django experts.

I am building a Django, DRF based mobile app and I want to have functionality of up votes and down votes for posts that user will post.

So what I want to say here that, if an user upvotes a post then it should be get higher ranks as quora questions do. and if there are more down votes than up votes then a post should be moved down ward rather than going up.

I have applied a logic already here and shared the screenshots as well. but I am sure that there is a better logic or solution for this problem.

Thanks in advance.

Mr Mike and Mr Lalit can you guide me here please?

[DJANGO DEVELOPER]

Is there anyone who can help me here?

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[oba stephen]

Hi, 

One way would be to create an extra field to track the difference in both fields and then in your meta information on that model set the ordering to that field. 

Another approach which is better is to do something like this. 

Votes.objects.extra(select={'diff': 'upvote - downvote'}).order_by('diff')

Best regards

Stephen Oba

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[DJANGO DEVELOPER]

Oba Thank you so much. and let me try it.

and one more thing that I want to ask that how can I calculate the up votes and down votes at the same time? as Facebook likes and dislikes do. can you guide me in this regard?

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[Chetan Ganji]

You should have a field on Votes Model diff_vote as integerfield, which will be updated when a user upvote or downvote. 

WHY?? 
Calculating this value on list view will result in higher latency. 
So we can dump that calculation on creating on updating.
 
What do you mean by calculate the up votes and down votes at the same time?

Regards,

Chetan Ganji

+91-900-483-4183

ganji....@gmail.com

http://ryucoder.in

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[DJANGO DEVELOPER]

Chetan I got what you're saying. so how diff_votes will be updated? do have I to apply the same logic as Oba discussed above?

and yes by calculating the up and down votes at the same time was that, if a user up votes my post and another user down votes my post then should be ranked accordingly.

means I just want to rank my post higher if there are more up votes than down votes. I think I have described well, what I want to apply at the moment.

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[Ryan Nowakowski]

On Thu, Jun 24, 2021 at 07:15:09AM -0700, DJANGO DEVELOPER wrote:
> Hi Django experts.
> I am building a Django, DRF based mobile app and I want to have
> functionality of up votes and down votes for posts that user will post.
> So what I want to say here that, if an user upvotes a post then it should
> be get higher ranks as quora questions do. and if there are more down votes
> than up votes then a post should be moved down ward rather than going up.
> I have applied a logic already here and shared the screenshots as well. but
> I am sure that there is a better logic or solution for this problem.

Do you want your users to be able to change or delete their vote?
In that case, you'll need to keep track of who voted what. Maybe create
a model like this:

class VoteQuerySet(models.QuerySet):

def down(self):
"""Return only the down votes"""
return self.filter(value__lt=0)

def up(self):
"""Return only the up votes"""
return self.filter(value__gt=0)

def down_total(self):
"""Return the down vote total as a negative number"""
return self.down().aggregate(Sum('value'))['value__sum']

def up_total(self):
"""Return the up vote total as a positive number"""
return self.up().aggregate(Sum('value'))['value__sum']

def total(self):
"""Return the total of all up and down votes"""
return self.aggregate(Sum('value'))['value__sum']


class Vote(models.Model):
"""A user's up or down vote for a post

"value" should be -1 for a down vote and 1 for an up vote

"""
user = models.ForeignKey(User, on_delete=models.CASCADE)
post = models.ForeignKey(Post, on_delete=models.CASCADE)
value = models.SmallIntegerField()

objects = VoteQuerySet.as_manager()

class Meta:
unique_together = (user, post)

def vote_up(self):
self.value = 1

def vote_down(self):
self.value = -1


You can then vote like this:

vote = Vote(user=user, post=post)
vote.vote_up() # or vote.vote_down()
vote.save()


Here's a post's up vote count:

post.vote_set.up_total()


You can change a user's vote like this:

vote = user.vote_set.get(post=post)
vote.vote_down()

... or delete:

vote.delete()


Any finally, here's how you can sort your posts:

Post.objects.all().annotate(vote_total=Sum('vote__value')).order_by('-vote_total')


Caveat: code untested



Hope this helps!

Ryan

[DJANGO DEVELOPER]

Ryan Thank you so much. I will give it try. and let you know about the results

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[Mike Dewhirst]

HE lmbo pop l9m6oo9k

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[DJANGO DEVELOPER]

Hi Mr Mike.

Can you please share you knowledge here to help me?

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