Question

If I have 2 interlinked models:

class Person(models.Model)
    name = models.CharField()

class Project(models.Model):
    person = models.ForeignKey(Person)
    title = models.CharField()

I frequently find myself trying to find the number of Projects associated with each Person:

person = Person.objects.get(id=1)
no_projects = Project.objects.filter(person=person).count()

Is there a way of adding this as a custom field to the Person model, such that I may just call person.no_projects?

Answer 1

This can be done by adding a property to the Person class.

class Person(models.Model)
    name = models.CharField()

    @property
    def no_projects(self):
        return Project.objects.filter(person=self).count()

This can be called now like this

person = Person.objects.get(id=1)
person.no_projects