Question

I’m having problem use Automatic Lightweight Migration Code in my App delegate !

I read all the apple’s documentations about “Automatic Lightweight Migration” but after all I can’t find my way to use the codes that is prepared to Automatic Lightweight Migration.

Recently, I just added some new Attribute to an Entity in my data model and I want to keep my old data.

my app delegate code is like 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];
    NSError *error = nil;

    NSDictionary *properties = [applicationFilesDirectory resourceValuesForKeys:[NSArray arrayWithObject:NSURLIsDirectoryKey] error:&error];

    if (!properties) {
        BOOL ok = NO;
        if ([error code] == NSFileReadNoSuchFileError) {
            ok = [fileManager createDirectoryAtPath:[applicationFilesDirectory path] withIntermediateDirectories:YES attributes:nil error:&error];
        }
        if (!ok) {
            [[NSApplication sharedApplication] presentError:error];
            return nil;
        }
    }
    else {
        if ([[properties objectForKey:NSURLIsDirectoryKey] boolValue] != YES) {
            // 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:@"FinancingPro.storedata"];
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:mom];
    if (![__persistentStoreCoordinator addPersistentStoreWithType:NSXMLStoreType configuration:nil URL:url options:nil error:&error]) {
        [[NSApplication sharedApplication] presentError:error];
        [__persistentStoreCoordinator release], __persistentStoreCoordinator = nil;
        return nil;
    }

    return __persistentStoreCoordinator;

Now I don’t know how to change this code to have Automatic Lightweight Migration !
Please Note that my db is NOT SQLlite.

Answer 1

You need to set the options dictionary with the NSInferMappingModelAutomaticallyOption key here:

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

By passing a nil value for options you are telling the store to ignore any migration.