property decorator eager load and eager load in general using Django

Question

Is it possible in Django to use eager loading for property decorator?

My code as example

class Player(models.Model):
    roles = models.ManyToManyField(Role, related_name='players')

    @property
    def role(self):
         return ", ".join([r.name for r in self.roles.all().order_by('name')])

When outputting the player role using the property, it runs a query each time.

Actually I still don't know how eager load works in general with Django. I can't find any good docs about it.

Thanks

Answer 1

This is a terminology issue. Django docs/source do not refer to "eager" loading as SQLAlchemy does. Instead, Django has select_related() and prefetch_related() filters for queries, which are documented in the QuerySet API reference.

But that is something you add to the query, not a declarative property. So you'd use prefetch_related('roles') when querying for the Player.

Answer 2

I'm not sure if this fits your needs, because this is useful for when you want to use the property of an instance several times, but Django has a @cached_property decorator which will cache the result of your property for as long as your instance exists.

More information if you do a quick ctrl+f in here:

https://docs.djangoproject.com/en/dev/ref/utils/