Annotate queryset with information if a particular foreign key exists

Question

Say I have two models like this:

from django.contrib.auth import User

class Post(models.Model):
  text = models.TextField()

class Like(models.Model):
  pos         


        

Answer 1

I ended up with a simpler approach, because I display Post objects in my views with pagination, so my Post's queryset is always quite small. Also, I display Post objects ordered by pk.

So my solution was building a python list of Post primary keys that request.user liked, chosen from posts I'm currently displaying (so the list will always be quite small):

pks = [ post.pk for post in queryset ]
first = pks[0]
last = pks[-1]
context['liked_posts'] = Like.objects.filter(user=request.user,
    post_id__range=sorted([first, last])).values_list('post_id', flat=True)

Then in my template I simply check if each Post pk is in the liked_posts list.

This approach requires only an extra query to the DB.