Core Data Migration and Versioning

Question

I followed this guide to implement the core data migration and versioning in my non–document-based application. I did as reported driving but when but when I start the application tells me that the model I am opening is not supported. How can I fix this?

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (_persistentStoreCoordinator) {
        return _persistentStoreCoordinator;
    }

    NSManagedObjectModel *mom = [self managedObjectModel];
    if (!mom) {
        NSLog(@"%@:%@ No model to generate a store from", [self class], NSStringFromSelector(_cmd));
        return nil;
    }

    NSFileManager *fileManager = [NSFileManager defaultManager];

    NSURL *applicationFilesDirectory = [self applicationFilesDirectory];
    NSURL *storeURL = [[self applicationFilesDirectory] URLByAppendingPathComponent:@"Preventivi.storedata"];

    NSError *error = nil;
    //Turn on automatic store migration
    NSMutableDictionary *optionsDictionary = [NSMutableDictionary dictionary];
    [optionsDictionary setObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption];
    NSDictionary *properties = [applicationFilesDirectory resourceValuesForKeys:@[NSURLIsDirectoryKey] error:&error];

    if (!properties) {
        BOOL ok = NO;
        if ([error code] == NSFileReadNoSuchFileError) {
            ok = [fileManager createDirectoryAtPath:[applicationFilesDirectory path] withIntermediateDirectories:YES attributes:nil error:&error];
            NSURL *defaultStoreURL = [[NSBundle mainBundle] URLForResource:@"Preventivi" withExtension:@"storedata"];
            if (defaultStoreURL) {
                [fileManager copyItemAtURL:defaultStoreURL toURL:storeURL error:NULL];
            }
        }
        if (!ok) {
            [[NSApplication sharedApplication] presentError:error];
            return nil;
        }
    } else {
        if (![properties[NSURLIsDirectoryKey] boolValue]) {
            // Customize and localize this error.
            NSString *failureDescription = [NSString stringWithFormat:@"Expected a folder to store application data, found a file (%@).", [applicationFilesDirectory path]];

            NSMutableDictionary *dict = [NSMutableDictionary dictionary];
            [dict setValue:failureDescription forKey:NSLocalizedDescriptionKey];
            error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:101 userInfo:dict];

            [[NSApplication sharedApplication] presentError:error];
            return nil;
        }
    }

    NSURL *url = [applicationFilesDirectory URLByAppendingPathComponent:@"Preventivi.storedata"];
    NSPersistentStoreCoordinator *coordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:mom];
    if (![coordinator addPersistentStoreWithType:NSXMLStoreType configuration:nil URL:url options:nil error:&error]) {
        [[NSApplication sharedApplication] presentError:error];
        return nil;
    }
    _persistentStoreCoordinator = coordinator;

    return _persistentStoreCoordinator;
}

Answer 1

Can you tell where the Application throws the error? If its in the last lines, you could try to change the storeType NSXMLStoreType to NSSQLiteStoreType for example.

if (![coordinator addPersistentStoreWithType:NSXMLStoreType configuration:nil URL:url options:nil error:&error])

to

if (![coordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:url options:options error:&error]) 

For this you have also to change the suffix to "sqlite".

NSURL *url = [NSURL fileURLWithPath: [applicationFilesDirectory stringByAppendingPathComponent: @"Preventivi.sqlite"]]

and

NSURL *defaultStoreURL = [[NSBundle mainBundle] URLForResource:@"Preventivi" withExtension:@"sqlite"];

Or if you already have a solution, you could share this :) But comparing with my code, there are no real differences (only have an option more

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                         [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                         [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

and you don't use the options while adding the persistent store ^^ )

I hope this helps :)

Answer 2

It seems you've configured your Core Data stack to use auto migration. And continued changing model without using versioning.

You have to use versioned model. If you didn't create a model version before modifying it, auto migration won't work. In order to make auto migration work before every modificaton you should create a new model version and modify that new version.

For example you want to add couple attributes to an entity and add another entity, you:

1. Create new model version (select model file, Editor->Add model version...);
2. Select that new version and add attributes and entity.

And you should also say if you use configurations or not, as far as auto migration has issues with configurations.