Open Radar

 
Summary:
I would like to create a subscription, which will send me notifications when record will be updated, but only that record which has non-empty `inviteCode` string field. Since there is no proper documentation about the restrictions for NSPredicate in comparison to Core Data's one, I spent hours to debug the problem, using well worked Core Data predicates as well some really fantastic ones. The results are listed below:

1. Predicate: NSPredicate * sPredicate = [NSPredicate predicateWithFormat:@"inviteCode != nil"];

Result: Error with description: "Expected constant value in comparison expression: inviteCode != nil"


2. Predicate: NSPredicate * sPredicate = [NSPredicate predicateWithFormat:@"length(inviteCode) > 0"];

Result: Crash with description: *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse function name 'length:' into supported selector (length:) '


3. Predicate: NSPredicate * sPredicate = [NSPredicate predicateWithFormat:@"inviteCode.lenght > 0"];

Result: Error with description: recordKey (inviteCode.lenght) contains invalid characters

4. Predicate: NSPredicate * sPredicate = [NSPredicate predicateWithFormat:@"inviteCode != \"\""];

Result: no errors in completion block, but subscription does not send any notifications after record with non-empty 'inviteCode' field gets updated.

Steps to Reproduce:
You must save "MyRecord" record with non-empty string field "myStringField" on either public or private database.
NSString * sID = @"subscription ID";
    NSPredicate * sPredicate = [NSPredicate predicateWithFormat:@"myStringField != nil"];
    CKSubscription * s = [[CKSubscription alloc] initWithRecordType:@"MyRecord" predicate:sPredicate subscriptionID:sID options:CKSubscriptionOptionsFiresOnRecordUpdate];
    
    CKNotificationInfo *note = [[CKNotificationInfo alloc] init];
    note.alertLocalizationKey = @"Notification text";
    s.notificationInfo = note;
    [database saveSubscription:s completionHandler...];

Expected Results:
The subscription created on a server and it will detect all updates of "MyRecord" records which field "myStringField" is not an empty string.

Proper documentation about all CloudKit's NSPredicate-related restrictions!

Actual Results:
Error with description: "Expected constant value in comparison expression: stringField != nil"

Version:
iOS 8+

Notes:


Configuration:
iPhone 5