What is the correct way to delete a UIManagedDocument?

Question

I can't seem to find any reliable documentation that explains the correct procedure for deleting a UIManagedDocument, and in particular one where the iCloud options have been turned ON.

I understand that this option would delete the file at this fileURL. And this would appear to be fine if iCloud is not being used.

[[NSFileManager defaultManager] removeItemAtURL:fileURL error:&error];

If iCloud is being used then CoreData creates files all over the place, including in /Document/CoreDataUbiquitySupport and in the iCloud /CoreData folder. So in this case is it up to me to call removeUbiquitousContentAndPersistentStoreAtURL for each store in the UIManagedDocument prior to calling [NSFileManager removeItemAtURL]. If so is this documented somewhere ?

[NSPersistentStoreCoordinator removeUbiquitousContentAndPersistentStoreAtURL:storeURL
                                                                     options:@{NSPersistentStoreUbiquitousContentNameKey:fileName,
   NSMigratePersistentStoresAutomaticallyOption:@YES,
         NSInferMappingModelAutomaticallyOption:@YES,
                          NSSQLitePragmasOption:@{ @"journal_mode" : @"DELETE" }}
                                                                       error:&error];

score 2 · Answer 1 · edited Feb 29 '16 at 19:10

Here is my two cents on the issue. I tried what dtrotzjr recommended and didn't have a whole lot of success. It seems that removeUbiquitousContentAndPersistentStoreAtURL:options:error: is great for clearing out data in a UIManagedDocument, but the Logs folder is still there and so are the remnants of the file I'm trying to delete. Here is a simpler method for completely deleting a UIManagedDocument from iCloud or Local Docs:

+ (void)deleteDocumentURL:(NSURL *)url{
    //if we have an iCloud Document, remove it from the UbiquitouseKeyValueStore
    if ([self isiCloudURL:url]) {
        [[NSUbiquitousKeyValueStore defaultStore] removeObjectForKey:[url lastPathComponent]];
    }

    //do the delete on another thread
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSFileCoordinator *coordinator = [[NSFileCoordinator alloc] initWithFilePresenter:nil];
        NSError *coordinationError;

        [coordinator coordinateWritingItemAtURL:url
                                    options:NSFileCoordinatorWritingForDeleting
                                      error:&coordinationError
                                 byAccessor:^(NSURL *newURL) {
         NSError *removeError;
        //code for performing the delete
        [[NSFileManager defaultManager] removeItemAtURL:newURL error:&removeError];

        //if we have an iCloud file...
        if ([self isiCloudURL:url]) {
            //remove log files in CoreData directory in the cloud
            NSURL *changeLogsURL = [[self urlForiCloudLogFiles] URLByAppendingPathComponent:[url lastPathComponent]];
                [[NSFileManager defaultManager] removeItemAtURL:changeLogsURL error:&removeError];
            }
        }];
    });
}

This is pretty much the code from Stanford's CS193 course 2012 + the delete for the changeLogs folder and it works on local and iCloud docs. Please let me know if you see any issues with performing the delete this way.

take a look at this link where I have posted some code examples and demo video's of how I got it working quite reliably. It shows the local directories and the iCloud directories being created and cleared.http://ossh.com.au/design-and-technology/software-development/uimanageddocument-icloud-integration/. — Duncan Groenewald, Dec 11 '13 at 22:43
Cool, thanks Duncan. This documentation looks real promising :) — Nathan Bruno, Dec 18 '13 at 17:20

score 1 · Accepted Answer · answered Oct 09 '13 at 02:33

1

For iCloud core-data content you want to call the static method removeUbiquitousContentAndPersistentStoreAtURL:options:error: on the NSPersistentStoreCoordinator class, then call removeItemAtURL:error:

See deleteManagedDocumentWithIdentifier: in my APManagedDocument project. This is on the ubiquitous_experiment branch which I am currently working on finalizing before I merge it back down to the master branch.

answered Oct 09 '13 at 02:33

dtrotzjr

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And is this supposed to remove the file from other devices too or am I supposed have logic in the app on other devices to detect that the file is no longer in iCloud and do the same thing on that device ? And what is the logic for detecting that the file has been removed ? Any documentation from Apple ? – Duncan Groenewald Oct 09 '13 at 05:26
The call to `removeUbiquitousContentAndPersistentStoreAtURL:options:error` will remove the Core Data transaction logs from iCloud and remove the persistent store file, the call to `removeItemAtURL:error` will remove the `UIManagedDocument` package. Now that I think about it since I store my documents in the ubiquitous store I need to `setUbiquitous:NO` the document first so that iCloud forgets about that as well. See WWDC 2013 Session 207 for more on `removeUbiquitousContentAndPersistentStoreAtURL:options:error` – dtrotzjr Oct 09 '13 at 14:45
Sure but what happens on other devices when the app starts up on them ? Bearing in mind they probably still have a working copy of the database, I don't see a notification in the documents for Core Data to tell us 'Oops someone deleted everything in the cloud, what do you want to do now: a) build a new copy and put it back in the cloud, b) keep your copy and make it local only, c) delete your copy too or d) let us decide ?" – Duncan Groenewald Oct 09 '13 at 23:27
This is just totally weird - now I have the mac online too !! This is nuts, I just open my existing sqlite files and then run migrate on the file, and thats it they're in the cloud, they don't even move anywhere themselves. Done, kaput! Too easy! I did have to turn off sandbox to open any file on the desktop. Core Data creates a CoreDataUbiquitySupport folder in the same directory as the document which has the fallback stores and stuff. Surely its not possible they have made it this easy. – Duncan Groenewald Oct 10 '13 at 00:47
Did you watch the WWDC Video? they have a callback that takes place when the persistentStore is going to be removed and or changed and the app is still running. – dtrotzjr Oct 10 '13 at 01:04
Yes, but I was under the impression it was only during startup! Reading the transcript again though... _"Now, I need to mention that this is a special case scenario. You will only see these notifications during our asynchronous setup process if there is no persistent store file on disk, or there are has been a change to the iCloud account **or the contents of the container since we last launched**."_ – Duncan Groenewald Oct 10 '13 at 03:06
Awesome, I had forgotten to set the persistentStore options, before opening prior to the delete but that's working fine now. I have just switched a bunch of my desktop files to iCloud and they have all migrated across fine too and some are around 100MB. – Duncan Groenewald Oct 10 '13 at 06:18

What is the correct way to delete a UIManagedDocument?

2 Answers2