Re: Need help on a (maybe complex) query with aggregate/annotate

On Feb 21, 6:11 am, Enrico <poe...@gmail.com> wrote:
> This query:
> Publisher.objects.filter(book__rating__gt=3.0).annotate(num_books=Count('bo ok'))
> returns all the publishers with at least one good book (ranked > 3)
> with annotated the number of good books for each publisher.
>
> How can i modify the query to get the list of ALL publishers with
> annotated the number of good books for each publisher?
> In other words I want to keep in the results also the Publishers
> without good books (num_books = 0).

Hi Enrico,

The Django documentation has an example of what you are trying to do:

https://docs.djangoproject.com/en/1.3/topics/db/aggregation/#generating-aggregates-for-each-item-in-a-queryset

The answer to your specific question is to do it this way:

qs = Publisher.objects.annotate(num_books=Count('book'))
for o in qs:
print o.num_books

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