Hay, i have a simple model

class Manufacturer(models.Model):
    name = models.CharField()
    car_count = models.IntegerField()

class Car(models.Model):
    maker = ForeignKey(Manufacturer)

I want to update the car_count field when a car is added to a manufacturer, I'm aware i could just count the Manufacturer.car_set() to get the value, but i want the value to be stored within that car_count field.

How would i do this?

EDIT

Would something like this work?

    def save(self):
        if self.id:
            car_count = self.car_set.count()
            self.save()