Re: Aggregating annotations

EDIT: 

the query should be:

Book.objects.values('rating').annotate(books_per_rating=Count('id')).aggregate(Max('books_per_rating'))

books_per_rating should be quoted in Max call.

On Friday, July 19, 2013 11:49:52 AM UTC+5:30, Debanshu Kundu wrote:

If I have a model Book defined as:

class Book(models.Model):     name = models.CharField(max_length=300)     pages = models.IntegerField()     price = models.DecimalField(max_digits=10, decimal_places=2)     rating = models.FloatField()     pubdate = models.DateField()

and I run the query:

Book.objects.values('rating').annotate(books_per_rating=Count('id')).aggregate(Max(books_per_rating))

I get a DatabaseError.

According to this https://docs.djangoproject.com/en/1.5/topics/db/aggregation/#aggregating-annotations, Django supports aggregating annotations. But in the example given in the link itself, they annotate over a QuerySet which in turn returns a QuerySet (and not ValuesQuerySet), so aggregate method runs successfully. But in my example aggregating a ValuesQuerySet raises a DatabaseError.

Is it a bug in Django? Because if Django does not support aggregation over ValuesQuerySet then it should raise an exception at Django level (not DatabaseError).

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