Need optimize query using annotate

Asked Jul 30 '18 at 15:20

Active Jul 30 '18 at 15:35

Viewed 59 times

Have 2 models : MyItem and Category

This works, but how do I do this with a single query using annotate:

for cat in Category.objects.all():
    cat.count = MyItem.objects.filter(category=cat).count()
    cat.save()

Like some:

Category.objects.annotate(_items_count=Count('myitem')).update(count=_items_count)

edited Jul 30 '18 at 15:35

asked Jul 30 '18 at 15:20

Roman Nozhenko

Except for the bracket, what is not working with this? – Willem Van Onsem Jul 30 '18 at 15:34
unresolved reference _items_count – Roman Nozhenko Jul 30 '18 at 15:36
Ah, what if you use `F('_items_count')` in the `update`? – Willem Van Onsem Jul 30 '18 at 15:36
Hmm, this should work on the idea, it's just in the data migration, I now have no way to check – Roman Nozhenko Jul 30 '18 at 15:39
@WillemVanOnsem `F('_items_count')` will give an error need use subquery. – Brown Bear Jul 30 '18 at 15:46
4

https://stackoverflow.com/questions/3652736/django-update-queryset-with-annotation – Brown Bear Jul 30 '18 at 15:47

0 Answers0