Archiving NSBlockPredicate and NSPredicate date functions
Archiving NSBlockPredicate and NSPredicate date functions
- Subject: Archiving NSBlockPredicate and NSPredicate date functions
- From: Dave DeLong <email@hidden>
- Date: Wed, 28 Apr 2010 14:13:32 -0600
Hi everyone,
I've figured out a way to do an "date in the last X days" predicate, but I'm having to do it as a block predicate. This works fine, but I've run up against another situation: NSBlockPredicates don't support archiving. This is a problem, since I need to store this predicate in a CoreData store.
Basically, I'm trying to do have a predicate like:
NSPredicate * p = [NSPredicate predicateWithFormat:@"%@ >= NOW() - 86400", aDate];
If that actually worked, it would return true if "aDate" is newer than 1 day ago (86400 seconds = 1 day).
I can do this with a block predicate:
NSTimeInterval timeAgo = -86400;
NSPredicate * p = [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary * bindings) {
NSDate * cutoff = [NSDate dateWithTimeIntervalSinceNow:timeAgo];
return ([cutoff laterDate:evaluatedObject] == evaluatedObject);
}];
....except that this can't be archived.
Is there a way around this? I'm not aware of any function like "NOW()" that can be used in an NSPredicate.
The only other way I've thought of is to use a substitution variable, something like $NOW, and then create my predicate dynamically using -predicateWithSubstitutionVariables:. This could work, except that some of my predicates get evaluated very frequently, and I'm worried about that being too costly. (However, if it's the only alternative, then I have no choice).
Thoughts? Suggestions?
Thanks!
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