How to join one table with grouped values from different query? - django

Question

I have a models like this:
class Subscription(models.Model):
visable_name = models.CharField(max_length=50, unique=True)
recipe_name = models.CharField(max_length=50)
website_url = models.URLField()
class User(models.Model):
username = models.CharField(max_length=50)
class UserSubs(models.Model):
subscription = models.ForeignKey(Subscription, to_field='visable_name')
user = models.ForeignKey(User, to_field='username')
And I want to prepare simple ranking, so I came up with something like this:
rank = UserSubs.objects.values('subscription').
annotate(total=Count('user')).
order_by('-total')`
what gives:
>> rank
[
{'total': 3, 'subscription': u'onet'},
{'total': 2, 'subscription': u'niebezpiecznik'},
{'total': 1, 'subscription': u'gazeta'}
]
what I need, is similar list of full objects:
[
{'total': 3, 'subscription': <Subscription: onet>},
{'total': 2, 'subscription': <Subscription: niebezpiecznik>},
{'total': 1, 'subscription': <Subscription: gazeta>}
]
I am not sure, whether 'select_related' will be helpful here, but I can't figured out how to use it :(

Answer 1

Better to build your query from Subscription because you need it:
Subscription.objects.annotate(total=models.Count('usersubs')).order_by('-total')

Answer 2

Maybe you can use dict and list comprehension, and filter this as simple python objects:
d = {sub.visable_name: sub for sub in Subscriptions.objects.all()}
new_rank = [
{
'total': row['total'],
'subscriptions': d[row['subscriptions']]
}
for row in rank
]
what will give:
>> new_rank
[
{'total': 3, 'subscriptions': <Subscriptions: onet>},
{'total': 2, 'subscriptions': <Subscriptions: niebezpiecznik>},
{'total': 1, 'subscriptions': <Subscriptions: gazeta.pl>}
]