Django queries: Count number of objects with FK to model instance
- by Chris Lawlor
This should be easy but for some reason I'm having trouble finding it. I have the following:
App(models.Model):
...
Release(models.Model):
date = models.DateTimeField()
App = models.ForeignKey(App)
...
How can I query for all App objects that have at least one Release?
I started typing:
App.objects.all().annotate(release_count=Count('??????')).filter(release_count__gt=0)
Which won't work because Count doesn't span relationships, at least as far as I can tell.
BONUS:
Ultimately, I'd also like to be able to sort Apps by latest release date. I'm thinking of caching the latest release date in the app to make this a little easier (and cheaper), and updating it in the Release model's save method, unless of course there is a better way.
Edit:
I'm using Django 1.1 - not averse to migrating to dev in anticipation of 1.2 if there is a compelling reason though.
