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I'm trying to fetch objects from core data that are not in a given set, but I haven't been able to get it to work. For instance, suppose that we have a core data entity named User, which has a few attributes such as userName, familyName, givenName, and active. Given an array of strings representing a set of usernames, we can easily fetch all the users corresponding to that list of usernames: NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] init]; NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"User" inManagedObjectContext:moc]; [request setEntity:entity]; NSArray *userNames = [NSArray arrayWithObjects:@"user1", @"user2", @"user3", nil]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"userName IN %@", userNames]; [request setPredicate:predicate]; NSArray *users = [moc executeFetchRequest:request error:nil]; However, I want to fetch the complement of that set, i.e., I want all the users in core data that don't have the usernames specified in the userNames array. Does anyone have an idea how to approach this issue? I thought it would be simple enough to add a "NOT" in the predicate (i.e., "userName NOT IN %@") , but Xcode throws an exception saying the predicate format could not be parsed. I also tried using the predicate builder available for fetch requests with no luck. The documentation wasn't particularly helpful either. Suggestions? Comments? Thanks for all your help :)

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