Finding posts in certain categories which you haven't voted on (django-voting, django-categories)

Question

I have an app where Posts are split into various categories using the django-categories app, using hard-linking (ForeignKey to categories.Category).

I am also using the django-voting app to allow users to vote_up or vote_down certain posts.

Now I have a view where I require the latest posts from a list of Categories (the users category whitelist) which the user has NOT voted on and they are not his own posts. How do I go about getting these posts in the most efficient manner from the DB query load perspective.

Here is my Post model:

class Post(models.Model):
    published = models.DateTimeField(default=datetime.now)
    author = models.ForeignKey(User, blank=True, null=True,
                               verbose_name='author', 
                               related_name='author_post')
    caption = models.CharField(max_length="240")
    image = models.ImageField(upload_to='user_images')
    up_votes = models.PositiveIntegerField(default=0)
    down_votes = models.PositiveIntegerField(default=0)
    category = models.ForeignKey('categories.Category')

Should I use RAW DB queries to get posts in reverse chronological order where the current logged in user hasn't voted and they aren't his own posts.

Answer 1

Depends on your db. If it's PosgtreSQL, you will be fine with subquery.

voted_already = (Vote.objects.filter(user=…, 
                                     content_type=…)
                             .values_list('object_id', flat=True))
not_voted = (Post.objects.filter(category__in=…)
                         .exclude(author=…, 
                                  pk__in=voted_already)
                         .order_by('-published'))