mergeWithCompletion on second device always completes with error: Error Domain=NSCocoaErrorDomain Code=3072 "The operation couldn’t be completed. (Cocoa error 3072.)"

[kunalsood]

Before I begin explaining this, I must say, I have a strong feeling that this is something I'm doing wrong.

The issue I have run into is, I'm having trouble getting a second device to do a mergeWithCompletion: successfully.

Here are the steps I've followed, several times..

• I add the framework to my project as per the instructions as per the README.md file.
• I import CoreDataEnsembles.h and CDEICloudFileSystem.h into my AppDelegate.
• Then, I add these to instance variables to my AppDelegate

    CDEPersistentStoreEnsemble *ensemble;
    CDEICloudFileSystem *cloudFileSystem;

• I set my AppDelegate to conform to the CDEPersistentStoreEnsembleDelegate protocol.
• Then, I add the following code in didFinishLaunchingWithOptions :-

    // Setup Ensemble
    cloudFileSystem = [[CDEICloudFileSystem alloc]
                       initWithUbiquityContainerIdentifier:my ubiquity container identifier];
    ensemble = [[CDEPersistentStoreEnsemble alloc] initWithEnsembleIdentifier:my ensemble identifier
                                                          persistentStorePath:path to my persistent store file
                                                        managedObjectModelURL:path to my managed object model (momd) file
                                                              cloudFileSystem:cloudFileSystem];
    ensemble.delegate = self;

    if (!ensemble.isLeeched)
    {
        [ensemble leechPersistentStoreWithCompletion:^(NSError *error) {
            if (error)
            {
                NSLog(@"Could not leech to ensemble: %@", error);
            }
            else
            {
                NSLog(@"Leeching succeeded");
            }
        }];
    }
    else
    {
        NSLog(@"isLeeched");
    }

Replacing my ensemble identifier, path to my persistent store file and path to my managed object model (momd) file with appropriate strings.

• I then add the following method, also in my AppDelegate :-

     - (void)persistentStoreEnsemble:(CDEPersistentStoreEnsemble *)ensemble didSaveMergeChangesWithNotification:(NSNotification *)notification
{
    [self.managedObjectContext performBlock:^{
        [self.managedObjectContext mergeChangesFromContextDidSaveNotification:notification];
    }];
}

• I also add the following method in various places throughout the app. (here, the ensemble being the one in my AppDelegate)

     NSLog(@"Attempting to merge");
    [ensemble mergeWithCompletion:^(NSError *error) {
        if (error)
        {
            NSLog(@"Error merging: %@", error);
        }
        else
        {
            NSLog(@"Merge succeeded");
        }
    }];

• Finally, I build and run the app on first device. On launch, the console logs :-

Leeching succeeded

and, then I add some information to manipulate the data in my core data store, and tap the button that calls mergeWithCompletion:, the console logs..

Attempting to merge
Merge succeeded

followed by the iCloud gauge showing upload activity.

• I build and run the app on second device, on launch, the console logs again :-

Leeching succeeded

• Then, tap the button that calls mergeWithCompletion: on the second device, the console logs..

Error merging: Error Domain=NSCocoaErrorDomain Code=3072 "The operation couldn’t be completed. (Cocoa error 3072.)"

• I repeat the process on third device, fourth device, and the simulator.. Same results.. i.e. On launch:

Leeching succeeded

Call mergeWithCompletion:

Error merging: Error Domain=NSCocoaErrorDomain Code=3072 "The operation couldn’t be completed. (Cocoa error 3072.)"

• I open my iCloud container, and do see the com.mentalfaculty.ensembles.clouddata directory, the ensemble identifier directory inside it, and the events and stores directories inside it, the events directory has a whole bunch of .cdeevent files, and the stores has what appear to be plist files for every device that leeched successfully. (So, I'm guessing this means that the first device did indeed sync successfully.) I have repeated this entire procedure several times, trying with different devices in different orders, and have not yet been able to get a second device to sync up.

Now, this is what <Foundation/FoundationErrors.h> says about 3072..

NSUserCancelledError = 3072,                                            // User cancelled operation (this one often doesn't deserve a panel and might be a good one to special case)

As cough nice cough an explanation as that is, I'm hoping someone might be able to tell me what I could be doing wrong here.

[drewmccormack]

I am pretty sure that the error you are seeing is just that the iCloud files have not been downloaded yet. Ensembles will request the files when it sees the metadata, and then it is up to iCloud to download. This part can take some time, and ensembles can't influence it. It is up to iCloud.

When the metadata for an iCloud file arrives, that file will seem to be in the file system, even if it hadn't been downloaded yet.

So what is happening is that ensembles is looking at the new files, trying to import them, and failing because one or more are not downloaded yet. In general, this is not a serious failure, and you should just retry a bit later.

I am surprised you can't get the sync to work at all. What if you are really patient, wait 15 minutes, and then try again?

Have you tested with the Idiomatic test app to see if that works?

Drew

[drewmccormack]

By the way, the cancelled error arises because ensembles uses a timeout to cancel file operations that take too long due to the file not yet being downloaded. We thought it was better just to fail the merge quickly and try later, rather than waiting for the download, which could take minutes or longer.

Drew

[kunalsood]

Confirmed, this was indeed the issue. Thanks for taking the time to explain this, and the improved error!!