ios - 多线程核心数据 - permanentStoreCoordinator 与 ParentContext

Question

我正在尝试解决由于从多个线程访问相同的 NSManagedObjectContext 而引起的问题。我在 Apple docs 中找到了以下内容:

let moc = … //Our primary context on the main queue

let privateMOC = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
privateMOC.parentContext = moc

privateMOC.performBlock {
    //...
}

这似乎是我所追求的。我还在 tutorial 中发现了一些非常相似的东西已针对 iOS 9 更新:

let privateContext = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
privateContext.persistentStoreCoordinator = coreDataStack.context.persistentStoreCoordinator

privateContext.performBlock { () -> Void in
  //...
}

他们似乎都实现了相同的目标，但是 Apple 文档的版本使用 parentContext 而不是直接使用 persistantStoreCoordinator。这两种方法有什么区别？

Answer 1

使用parentContext。自 iOS 5 以来，这优于使用持久存储协调器的方法。

Prior to OS X v10.7 and iOS v5.0, the parent store is always a persistent store coordinator. In OS X v10.7 and later and iOS v5.0 and later, the parent store may be another managed object context. Ultimately the root of a context’s ancestry must be a persistent store coordinator. The coordinator provides the managed object model and dispatches requests to the various persistent stores containing the data.

在您的特定情况下:

If a context’s parent store is another managed object context, fetch and save operations are mediated by the parent context instead of a coordinator. This pattern has a number of usage scenarios, including:

• Performing background operations on a second thread or queue.

来源:NSManagedObjectContext 类引用，“Parent Store”。