SOLVED: NSSortDescriptor with NSSet count?

Forums > iOS

@EpiGardenia

May '21

Is it possible to sort by the counts of one NSSet of entity?

For example:

Project

Items (to-many)

In NSPredicate, it is possible to useitems.@count, but this form get error in NSSortDescriptor keypath.

( NSSortDescriptor(key: "items.@count", ascending: ascending))

items.count will also fail,

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'to-many key not allowed here'

Does it mean it is Impossible to sort by counts with NSSortDescriptor?

@delawaremathguy

May '21

hi,

had you considered adding a derived attribute to the entity (on the one-side of the relationship) named itemCount to keep the count of items (on the to-many side of the relationship)? that might solve the sort descriptor issue.

see WWDC2019 video Session 230, Making Apps with Core Data at around the 19:00 mark.

hope that helps,

DMG

@EpiGardenia

May '21

That's brilliant idea, thank you so much!

Thank you for finding the video with timestamp for me too, didn't know that before ( mainly start 2020) , now I learnt new things :)

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