Переименовать файл xcdatamodel

Что нужно сделать, чтобы переименовать файл .xcdatamodel. Переименование файла .xcdatamodel вместе с изменением ...

NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"newfilename" withExtension:@"momd"];
__managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];    
return __managedObjectModel;

и

NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"newfilename.sqlite"];

не работает! Я получаю следующую ошибку:

2011-04-11 17:19:54.164 ProjectName[5826:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Cannot create an NSPersistentStoreCoordinator with a nil model'
*** Call stack at first throw:
(
    0   CoreFoundation                      0x00fa15a9 __exceptionPreprocess + 185
    1   libobjc.A.dylib                     0x010f5313 objc_exception_throw + 44
    2   CoreData                            0x00013853 -[NSPersistentStoreCoordinator initWithManagedObjectModel:] + 419
    3   ProjectName                         0x00003471 -[ProjectNameAppDelegate persistentStoreCoordinator] + 257
    4   ProjectName                         0x000031a4 -[ProjectNameAppDelegate managedObjectContext] + 100
    5   ProjectName                         0x000028ca -[ProjectNameAppDelegate makeSplitViewController] + 762
    6   ProjectName                         0x00002d44 -[ProjectNameAppDelegate application:didFinishLaunchingWithOptions:] + 68
    7   UIKit                               0x001f3c89 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1163
    8   UIKit                               0x001f5d88 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 439
    9   UIKit                               0x00200617 -[UIApplication handleEvent:withNewEvent:] + 1533
    10  UIKit                               0x001f8abf -[UIApplication sendEvent:] + 71
    11  UIKit                               0x001fdf2e _UIApplicationHandleEvent + 7576
    12  GraphicsServices                    0x018f9992 PurpleEventCallback + 1550
    13  CoreFoundation                      0x00f82944 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
    14  CoreFoundation                      0x00ee2cf7 __CFRunLoopDoSource1 + 215
    15  CoreFoundation                      0x00edff83 __CFRunLoopRun + 979
    16  CoreFoundation                      0x00edf840 CFRunLoopRunSpecific + 208
    17  CoreFoundation                      0x00edf761 CFRunLoopRunInMode + 97
    18  UIKit                               0x001f57d2 -[UIApplication _run] + 623
    19  UIKit                               0x00201c93 UIApplicationMain + 1160
    20  ProjectName                         0x00002599 main + 121
    21  ProjectName                         0x00002515 start + 53
)
terminate called after throwing an instance of 'NSException'

Примечание: я использую Xcode4.