CODEWITHSUNDEEP
djangodjango-models
Sreekar Mouli
Sreekar Mouli

Reputation: 1432

django - order by query

I have a model called Post which has two fields upvotes and downvotes. Now, upvotes, downvotes are ManyToManyField to a User. This is the model:

class Post(models.Model):
    profile = models.ForeignKey(Profile, on_delete=models.CASCADE)
    title = models.CharField(max_length=300)
    content = models.CharField(max_length=1000)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    subreddit = models.ForeignKey(Subreddit, on_delete=models.CASCADE)
    upvotes = models.ManyToManyField(Profile, blank=True, related_name='upvoted_posts')
    downvotes = models.ManyToManyField(Profile, blank=True, related_name='downvoted_posts')

I have to make a query where I have to get all posts sorted by

total (upvotes) - total (downvotes)

I have tried Post.objects.order_by(Count('upvotes')) to get started but there's an error.

Upvotes: 2

Views: 52

Answers (1)

Håken Lid
Håken Lid

Reputation: 23064

Use QuerySet.annotate() first.

Post.objects.annotate(
    total_votes=Count('upvotes')-Count('downvotes')
).order_by('total_votes')

An added benefit of annotate() is that every Post in the queryset gets the total_votes attribute, which you can access later with no additional database query or calculation.

Upvotes: 2

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