How to count the number of specific objects in a Django model?

Question

I have a Django model called User and would like to count how many items are within the following object.

class User(AbstractUser):
    following = models.ManyToManyField("self", related_name="followers")

I have tried counting them using this line followers_num = User.following.count(), but I receive this error 'ManyToManyDescriptor' object has no attribute 'count'.

I have also tried followers_num = User.objects.all().count(), but that returns the number of users.

Does anyone know how to do this?

willeM_ Van Onsem · Accepted Answer · 2022-07-08 21:36:43Z

1

You can count the total number of following relations with:

User.following.through.objects.count()  # total number of following relations

If you want to add an extra attribute to the User objects with the number of followings per User, you can use:

from django.db.models import Count

User.objects.annotate(
    num_following=Count('following')  # number of following per (!) user
)

Note: A ManyToManyField ^[Django-doc] to itself is by default symmetrical, so that means that if A is a following of B, then B is automatically a following of A, you likely do not want that. You can turn this off with symmetrical=False ^[Django-doc].

edited Jul 8, 2022 at 21:36

answered Jul 8, 2022 at 21:31

willeM_ Van Onsem

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2 Comments

econo Over a year ago

I added symmetrical=False and ran migrations, but I do not think anything happened. When I count how many are following and how many followers a user has, both values change if a new user follows that particular user. Will I have to delete all the existing users?

willeM_ Van Onsem Over a year ago

@econo: no, the number of following/follower relations are always the same. symmetrical=False is about how Django handles adding/removing/... items in such ManyToManyField relations.

Ayman · Accepted Answer · 2022-07-08 22:06:29Z

0

I will suppose you want to get the user followers so you will First find the User

user = User.objects.get(pk=1)
user.following.all() # this will get you the followers of this user

user count to get their count, comment if that doesn't match what you need

edited Jul 8, 2022 at 22:06

answered Jul 8, 2022 at 21:32

Ayman

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2 Comments

willeM_ Van Onsem Over a year ago

This does not work for exactly the same reason as in the question: because User.following is a ManyToManyDescriptor, not a QuerySet or manager...

Ayman Over a year ago

I am sorry I am wrong I didn't focus I will edit it

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