DjangoQueryProblem.markdown

Hey, Django rookie here.

I have this model, comments are managed with the django_comments contrib:

class Fortune(models.Model):
    author = models.CharField(max_length=45, blank=False)
    title = models.CharField(max_length=200, blank=False)
    slug = models.SlugField(_('slug'), db_index=True, max_length=255, unique_for_date='pub_date')
    content = models.TextField(blank=False)
    pub_date = models.DateTimeField(_('published date'), db_index=True, default=datetime.now())
    votes = models.IntegerField(default=0)
    comments = generic.GenericRelation(
        Comment,
        content_type_field='content_type',
        object_id_field='object_pk'
    )

I want to retrieve Fortune objects with a supplementary nb_comments value for each, counting their respectve number of comments ; I try this query:

>>> Fortune.objects.annotate(nb_comments=models.Count('comments'))

From the shell:

>>> from django_fortunes.models import Fortune
>>> from django.db.models import Count
>>> Fortune.objects.annotate(nb_comments=Count('comments'))
[<Fortune: My first fortune, from NiKo>, <Fortune: Another One, from Dude>, <Fortune: A funny one, from NiKo>]
>>> from django.db import connection
>>> connection.queries.pop()
{'time': '0.000', 'sql': u'SELECT "django_fortunes_fortune"."id", "django_fortunes_fortune"."author", "django_fortunes_fortune"."title", "django_fortunes_fortune"."slug", "django_fortunes_fortune"."content", "django_fortunes_fortune"."pub_date", "django_fortunes_fortune"."votes", COUNT("django_comments"."id") AS "nb_comments" FROM "django_fortunes_fortune" LEFT OUTER JOIN "django_comments" ON ("django_fortunes_fortune"."id" = "django_comments"."object_pk") GROUP BY "django_fortunes_fortune"."id", "django_fortunes_fortune"."author", "django_fortunes_fortune"."title", "django_fortunes_fortune"."slug", "django_fortunes_fortune"."content", "django_fortunes_fortune"."pub_date", "django_fortunes_fortune"."votes" LIMIT 21'}

Below is the properly formatted sql query:

SELECT "django_fortunes_fortune"."id", 
       "django_fortunes_fortune"."author", 
       "django_fortunes_fortune"."title", 
       "django_fortunes_fortune"."slug", 
       "django_fortunes_fortune"."content", 
       "django_fortunes_fortune"."pub_date", 
       "django_fortunes_fortune"."votes", 
       COUNT("django_comments"."id") AS "nb_comments" 
FROM "django_fortunes_fortune" 
LEFT OUTER JOIN "django_comments" 
    ON ("django_fortunes_fortune"."id" = "django_comments"."object_pk") 
GROUP BY "django_fortunes_fortune"."id", 
         "django_fortunes_fortune"."author", 
         "django_fortunes_fortune"."title", 
         "django_fortunes_fortune"."slug", 
         "django_fortunes_fortune"."content", 
         "django_fortunes_fortune"."pub_date", 
         "django_fortunes_fortune"."votes" 
LIMIT 21

Can you spot the problem? Django won't LEFT JOIN the django_comments table with the content_type data (which contains a reference to the fortune one).

How could I remedy this and make Django doing the expected query?

Hint: I'm using Django 1.2-DEV

Thanks in advance for your help.

Yeah, you are right raw SQL is always a bad solution, if you find the answer let me know.

thoas> I checked out twice but the sql query - even if quite heavy and especially ugly for what it does, works... though on SQLite. What RDBMS are you using?