how to do a select max in django

Question

I have a list of objects how can I run a query to give the max value of a field:

I'm using this code:

def get_best_argument(self):
        try:
            arg = self.argument_set.order_by('-rating')[0].details
        except IndexError:
            return 'no posts'
        return arg

rating is an integer

Answer 1

See this. Your code would be something like the following:

from django.db.models import Max
# Generates a "SELECT MAX..." statement
Argument.objects.all().aggregate(Max('rating'))

If you've already gotten the list out of the database, then you'd do something like this:

from django.db.models import Max
args = Argument.objects.all()
# Calculates the maximum out of the already-retrieved objects
args.aggregate(Max('rating'))

This is untested so I may have made a mistake somewhere, but there you go.