django - Idiomatic way of counting number of related objects -

this how doing currently:

class article(models.model):      ...      def nr_notes(self):         return len(note.objects.filter(article=self.pk))   class note(models.model):     article = models.foreignkey(article, on_delete=models.cascade) 

but thought "there must better way". accessing the generated notes_set field?

what right way implement method nr_notes?

yes, use count, count query on database rather evaluating filter

 note.objects.filter(article=self.pk).count() 

from evaluating querysets:

a queryset evaluated when call len() on it. this, might expect, returns length of result list.

note: if need determine number of records in set (and don’t need actual objects), it’s more efficient handle count @ database level using sql’s select count(*). django provides count() method precisely reason.