How to get Count of objects by aggregate within Queryset class

Question

i want to get object that is Maximum length/count of ManyToMany Field

class Member(models.Model):
    pass

class Chatroom(models.Model):
    ...
    members = models.ManyToMany(Member)
    ...

chatRoom = Chatroom.objects.aggregate(Max('members'))
### {'members__max':15}

this code does not return an object like:class <QuerySet [object]> but i want to take an object to do something so i did do this

room = ChatRoom.objects.aggregate(max_value=Max('members')).get(members__count=max_value)

its got an Error : it says there is no __count look up.. could you help me please...

Do you simply want the ChatRoom with the most members? Note that Max('members') will not do what you assume it does, it will only give the maximum id of the Member table. — Abdul Aziz Barkat
– Abdul Aziz Barkat, Commented Jun 12, 2021 at 8:16

willeM_ Van Onsem · Accepted Answer · 2021-06-12 08:21:10Z

1

Likely the easiest way to obtain the Chatroom with the largest number of members is with:

from django.db.models import Count

Chatroom.objects.annotate(
    nmembers=Count('members')
).order_by('-nmembers').first()

Since django-3.2, you can work with .alias(…) [Django-doc] to prevent calculating the number of members twice:

from django.db.models import Count

Chatroom.objects.alias(
    nmembers=Count('members')
).order_by('-nmembers').first()

answered Jun 12, 2021 at 8:21

willeM_ Van Onsem

482k33 gold badges483 silver badges624 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to get Count of objects by aggregate within Queryset class

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related