python - Sum if in Django ORM -

python - Sum if in Django ORM -

i have 2 models: publisher , book.

i retrieving publishers with

publisher.objects.filter(name="a").annotate(total_pages=sum('books__num_pages'))

but interested in total sum of number of pages books written in 2014.

i not familiar options create sumif in django. how others solve problem?

i think there should possibility like

sum('books__num_pages', where={'year': 2014})

or that.

books_num_pages = books.objects.filter(publisher__name='a', year=2014).aggregate(sum('num_pages'))

python django django-models django-forms django-views