How to count the value of dictionary using queryset in django

Question

I used .value('post_id') in django to bring the following values.

<QuerySet [{'post_id': 3}, {'post_id': 2}, {'post_id': 1}, {'post_id': 3}]>

If you count the value of each dictionary, you will have one, one, and two, respectively. Which queryset should I look for, instead of counting it as a queryset without for loop ?

models.py

class Like (models.Model) :
    liked_people = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, null=True)
    post = models.ForeignKey(Post, on_delete=models.CASCADE, related_name='liked_people', null=True)

https://stackoverflow.com/questions/629551/how-to-query-as-group-by-in-django do you mean this? — Alvi15, Oct 28 '20 at 11:06
Share the relevant model. You should annotate the referred model instead. — Willem Van Onsem, Oct 28 '20 at 11:09
There are two 'post_id's with a value of 3, and one 'post_id' with a value of one or two. I mean, I wonder if there's a queryset like this that can get the number of value. — leedjango, Oct 28 '20 at 11:26
@leedjango: can you please share the model where this queryset comes from? — Willem Van Onsem, Oct 28 '20 at 11:26

score 1 · Accepted Answer · answered Oct 28 '20 at 11:34

You should annotate the target model, so:

from django.db.models import Count

Post.objects.annotate(
    number_of_liked=Count('liked_people')
)

The Post objects that arise from this will have an extra attribute .number_of_liked that contains the number of related Likeds.

You can further filter the Like objects, for example with:

from django.db.models import Count

Post.objects.filter(
    liked_people__liked_people=my_user
).annotate(
    number_of_liked=Count('liked_people')
)

This will exclude Post objects that have no related Like objects with liked_people=my_user. You can also include these, but then with .number_of_liked = 0, with:

from django.db.models import Count, Q

Post.objects.annotate(
    number_of_liked=Count(
        'liked_people',
        filter=Q(liked_people__liked_people=my_user)
    )
)

How to count the value of dictionary using queryset in django

1 Answers1