Hi,
I'm trying to use aggregation to count the number of "likes" on an item.
The likes for an item are stored in a related model, called LikeStatus:
class Item(models.Model):
> ...
> class ItemLikeStatus(models.Model):
> LIKE_STATUS_CHOICES = (
> ('L', 'Liked'),
> ('U', 'Unliked'),
> ('A', 'Abstained (no vote)'),
> ('N', 'Not seen yet'),
> )
> user = models.ForeignKey(User)
> item = models.ForeignKey(Item)
> liked_status = models.CharField(max_length=1,
> choices=LIKE_STATUS_CHOICES)
I'm using the following aggregation:
items_by_popularity =
> Item.objects.all().annotate(Count('itemlikestatus')).order_by('-itemlikestatus__count')[:number_requested]
However, I would like to count up only the like statuses where the
liked_status code is "L".
My thoughts are that I can iterate through the entire Item set myself and
do a filter on the related itemlikestatus for each Item, and produce the
aggregation by hand. However, that seems like a silly way to do it, and
doesn't really use the database.
I was wondering if there's a smarter way to still use aggregation, but
filter out to only count a subset of related ItemLikeStatus?
Cheers,
Victor
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