Django equivalent of COUNT with GROUP BY

Question

I know Django 1.1 has some new aggregation methods. However I couldn\'t figure out equivalent of the following query:

SELECT player_type, COUNT(*) FROM playe         


        

Answer 1

Django 1.1 does support aggregation methods like count. You can find the full documentation here.

To answer your question, you can use something along the lines of:

from django.db.models import Count
q = Player.objects.annotate(Count('games'))
print q[0]
print q[0].games__count

This will need slight tweaking depending on your actual model.

Edit: The above snippet generates aggregations on a per-object basis. If you want aggregation on a particular field in the model, you can use the values method:

from django.db.models import Count
q = Player.objects.values('playertype').annotate(Count('games')).order_by()
print q[0]
print q[0].games__count

order_by() is needed because fields that are in the default ordering are automatically selected even if they are not explicitly passed to values(). This call to order_by() clears any ordering and makes the query behave as expected.

Also, if you want to count the field that is used for grouping (equivalent to COUNT(*)), you can use:

from django.db.models import Count
q = Player.objects.values('playertype').annotate(Count('playertype')).order_by()
print q[0]
print q[0].playertype__count