iOS Predicate for RLMLinkingObjects (Realm)

Question

I have linking object in my category.

@property (readonly) RLMLinkingObjects *relatedAttachments;

I only want to take category if it have relatedAttachments. I try with this.

NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"relatedAttachments.count > 0"]];

self.categories = [[Category objectsWithPredicate:pred] sortedResultsUsingProperty:@"id" ascending:YES];

I got error like this.

RLMPrecondition(property, @"Invalid property name",

So I try with other.

NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"relatedAttachments.count!=nil"]];
NSPredicate *pred = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"relatedAttachments.count!=NULL"]];

But it is still not okay. How shall I do?

Answer 1

You're looking for a predicate like:

[NSPredicate predicateWithFormat:@"relatedAttachments.@count > 0"];

@count is a collection operator that evaluates to the number of elements in the collection it appears to the right of.