ios - Realm query sum of property -

i'm using realmswift , have realm object called book

book ===== title: string pagecount: int 

when app starts books using:

allbooks = realm.objects(book) 

a book has realm property called pagecount

i'm trying understand how can total pages count books?

so if have book 3 pages, book b 11 pages , book c 0 pages total count 3+11+0 = 14

i préfère doing query , not iterate through books

you can total number of pages book objects follows:

let totalpages: int = realm.objects(book).sum("pagecount")