为CoreData添加版本管理

/** Returns the persistent store coordinator for the application. If the coordinator doesn't already exist, it is created and the application's store added to it. */- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {    if (persistentStoreCoordinator_ != nil) {        return persistentStoreCoordinator_;    }        NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"golf.sqlite"];        NSError *error = nil;    persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];            NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:                             [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,                             [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];         if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType                                                   configuration:nil                                                              URL:storeURL                                                          options:options                                                            error:&error]) {                NSLog(@"Unresolved error %@, %@", error, [error userInfo]);        abort();    }            return persistentStoreCoordinator_;}