iphone - NSPredicate with functions or selectors

Question

I have a lot of people NSManagedObjects that I need filtering and was hoping to do it within the initial fetch instead of filtering the array afterwards. I've used selectors in predicates before, but never when fetching NSManagedObjects, for example I have all my employees and then i use this predicate on the NSArray...

[NSPredicate predicateWithFormat:@"SELF isKindOfClass:%@", [Boss class]]

...but now I want to do a bit more math based on different attributes of my objects. I thought I could do something like...

[NSPredicate predicateWithFormat:@"SELF bonusIsAffordable:%f", howMuchMoneyTheCompanyHas];

..where bonusIsAffordable: is a method of my Employee class and would calculate whether I can afford to pay them a bonus. But I get an error...

Unknown/unsupported comparison predicate operator type cocoa

Any ideas what I'm screwing up?

Answer 1

This gets a whole lot easier with Blocks:

NSPredicate *bossPred = [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {

    return [evaluatedObject isKindOfClass:[Boss class]];
}];