Hi all,
I stole some code from this posting:
http://groups.google.com/group/django-users/msg/82a9c2e94ff05188
And then I used it to calculate the rating averages of my songs like
so:
models.py:
=======
class Song(models.Model):
...
songrtng = models.ManyToManyField(Rating)
...
class Rating(models.Model):
...
score = models.IntegerField(default=0)
...
views.py:
======
songlist = Song.objects.all().extra(
select={
'avg': 'SELECT AVG(song_rating.score) FROM
song_rating \
WHERE song_rating.song_id = song_song.id \
AND song_rating.score IS NOT NULL',
}
)
template:
=======
{% for currentsong in songlist %}{{ currentsong.id }}:
{{ currentsong.avg }}<br>{% endfor %}
This works beautifully. It's cool when I want the avg rating score for
each song in a certain queryset.
My prob now is that when I already have a specific song (i.e., not
just a subset of songs filtered from all songs), I still need to use
songlist first, filter it down to my specific song's id via id__exact
and take the index [0], and only then its avg. Of course this also
works, but I feel kinda dumb using it that way, so...:
My question is: isn't there a more straight-forward way? I mean, I
know Django has no aggregation support, but still, even with custom
SQL, there must be a DRYer cleaner more elegant way get the rating
score average at the level of an individual song.
If a already have the song instance, I have no idea how to the
respective SQL on it to get what I want since the extra() stuff works
on queries.
Any help greatly appreciated!
EE
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