Question

For example lets say I have a model named “ClassRoom” and a model named “Student” and Student has a foreign key relationship with ClassRoom.

Class Student(models.Model):
    classroom = models.ForeignKey(ClassRoom, related_name='student')

How can I Find which class room has the most students in it with a basic Django query. What I did to find the answer seems like it should be easier.

max = 0    
for c in ClassRoom.objects.all():
        if c.student.count() > max:
            print 'ID: %s' % c.id
            max = c.student.count()

and I would then take the last ID printed and do a .get() query on the class room ID. Is there anyway to do this with annotation or aggregate perhaps?

Answer 1

Try adding something like this to your ClassRoom object:

def num_students(self):
    return Students.objects.filter(classroom=self).count()

Obviously replace classroom with whatever you called it. Then you should be able to use the __max query.

Disclaimer: I haven’t tried this, but it works in my head 🙂