在哪里放置代码 配置持久存储以进行迁移

Question

我已经创建了一个 Mac 应用程序并在 App Store 上分发给许多客户，我需要向核心数据模型添加一个属性。我阅读了 Apple 提供的文档，可在此处获取。

但是，它提供了这段代码来启用自动迁移：

NSError *error;
NSPersistentStoreCoordinator *psc = <#The coordinator#>;
NSURL *storeURL = <#The URL of a persistent store#>;
NSDictionary *optionsDictionary =
    [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES]
                    forKey:NSMigratePersistentStoresAutomaticallyOption];

NSPersistentStore *store = [psc addPersistentStoreWithType:<#Store type#>
                                configuration:<#Configuration or nil#>
                                URL:storeURL
                                options:optionsDictionary
                                error:&error];

..而且我不知道该把它放在哪里。有人提到（在另一个线程中）它进入了 PersistentStoreCoordinator，但是，我只是使用默认的 Cocoa 应用程序模板并启用了“使用核心数据进行存储”。我必须创建自己的 AppDelegate，但从未见过任何有关 PersistentStoreCoordinator 的内容（现在仍然没有。我尝试创建一个新应用程序只是为了检查）。这里有什么帮助吗？我是 Cocoa 的新手，但我的应用程序在没有 PersistentStoreCoordinator 的情况下工作得很好，这就是为什么我还没有实现它。我确实创建了一个 AppDelegate，但是当我将这段代码放在那里时，它会抛出许多错误。帮助：/

编辑（昵称）：这是新代码：

我的头文件：

Answer 1

在这里，您可以：核心数据相关标头和方法。

应用程序委托标头 - 核心数据相关部分

@interface CoreDataFirstStepsAppDelegate : NSObject <UIApplicationDelegate> 
{    
     // ...
@private
    NSManagedObjectContext *managedObjectContext_;
    NSManagedObjectModel *managedObjectModel_;
    NSPersistentStoreCoordinator *persistentStoreCoordinator_;
}

// ...

@property (nonatomic, retain, readonly) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;

应用程序委托实现 - 核心数据相关部分

/**
 Returns the managed object context for the application.
 If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
 */
- (NSManagedObjectContext *)managedObjectContext {

    if (managedObjectContext_ != nil) {
        return managedObjectContext_;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        managedObjectContext_ = [[NSManagedObjectContext alloc] init];
        [managedObjectContext_ setPersistentStoreCoordinator:coordinator];
    }
    return managedObjectContext_;
}


/**
 Returns the managed object model for the application.
 If the model doesn't already exist, it is created from the application's model.
 */
- (NSManagedObjectModel *)managedObjectModel {

    if (managedObjectModel_ != nil) {
        return managedObjectModel_;
    }
    NSString *modelPath = [[NSBundle mainBundle] pathForResource:@"CoreDataFirstSteps" ofType:@"momd"];
    NSURL *modelURL = [NSURL fileURLWithPath:modelPath];
    managedObjectModel_ = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];    
    return managedObjectModel_;
}


/**
 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:@"CoreDataFirstSteps.sqlite"];

    NSError *error = nil;
    persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {

        NSError *error;
        NSURL *storeURL = storeURL;
        NSPersistentStoreCoordinator *psc = persistentStoreCoordinator_;
        NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                                 [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                                 [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

        if (![psc addPersistentStoreWithType:NSSQLiteStoreType
                               configuration:nil
                                         URL:storeURL
                                     options:options 
                                       error:&error]) 
        {
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }       
    }    

    return persistentStoreCoordinator_;
}

/**
 Returns the URL to the application's Documents directory.
 */
- (NSURL *)applicationDocumentsDirectory {
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}