Django query aggregation - django

Question

Imagine a number guessing game where one person thinks of a number and another person has to guess it. The game is over if the correct number was guessed.
The models might look like this
class SecretNumber(models.Model):
number = models.IntegerField()
class Guess(models.Model)
secretnumber = models.Foreignkey(SecretNumber)
guess = models.IntegerField()
After having played four times, the database might look like this:
id number
==========
1 10
2 54
3 68
4 25
id secretnumber_id guess
=============================
1 1 50
2 1 30
3 1 10
4 2 99
5 2 60
6 2 54
7 3 1
8 3 68
9 4 73
10 4 34
11 4 86
12 4 51
13 4 25
As you can see, the guesser was very lucky: it took him 3, 3, 2 and 4 guesses. But that's just to keep this example short.
Now I need to come up with a query which will allow to display the following data:
Nb. guesses Count
=====================
2 1
3 2
4 1
A manual SQL statement would look something like this:
SELECT inner_count AS 'Nb. guesses', count(inner_count) AS 'Count' FROM (
SELECT secretnumber_id, count(id) AS inner_count FROM guess GROUP BY secretnumber_id
) GROUP BY inner_count
I thought about annotating an annotation, but this seems not to be possible.
Any ideas?

Answer 1

If you're using django (ie models instead of classes), you want to use the QuerySet aggregate functions
e.g.
from django.db.models import Count
guesses = Guess.objects.values('secretnumber').annotate(Count('secretnumber'))
This will give you a queryset with a list of objects, which have a secretnumber and a count value.