Django查询获取相关集数

Question

I am querying the db and am trying to find the count of a related set named 'item'.

user_lists = List.objects.filter(user=user).select_related('city','city__country')

that brings up the items I want, but to add the count of the related set, I'm adding annotate:

user_lists = List.objects.filter(user=user).select_related('city','city__country').annotate(item_count=Count('item'))

However, this returns an empty query from the db. Any ideas why? I'm not getting any errors. Just an empty query set.

Answer 1

Not an actual answer, just an idea on how you can investigate: check the actual query, that's being executes via print str(some_queryset.query) . Then you could try executing the query in manage.py dbshell and check the results.

Also posting your models and db engine might be useful, as it might be related.

Answer 2

maybe you can use count() method to count items in a QuerySet: count()

user_lists_count = List.objects.filter(user=user).select_related('city','city__country').count()

is this working ?

hope this is what you want.

Answer 3

Just realized it was an issue with the item_count variable. When I used total_items it worked fine.