奇怪的父/子NSManagedObjectContext现象 [英] Strange parent / child NSManagedObjectContext phenomenon
问题描述
我已经创建了两个这样的上下文：
I have created two context like this:
// create writer MOC
_privateWriterContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
[_privateWriterContext setPersistentStoreCoordinator:_persistentStoreCoordinator];
// create main thread MOC
_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
_managedObjectContext.parentContext = _privateWriterContext;
我有一个 NSFetchResultedController c $ c> _managedObjectContext 。
I have a NSFetchResultedController initiated with _managedObjectContext.
我知道这很奇怪，但我添加一个记录到父 _privateWriterContext ，我保存。
I know it is strange, but I am adding a record to the parent to _privateWriterContext, I am saving it.
令人惊讶的是，因此 FRC 会收到有关此事件的通知。为什么？我没有重置的孩子，或任何其他。我认为他们是独立的实体，只要孩子的上下文不会得到保存。
What is surprising is that child context and so FRC gets notified about this event. Why? I have not reset-ed child, or anything else. I thought they are independent entities as long as child context will not get saved.
在@pteofil文章我发现这行：
In @pteofil article I found this line:
当在上下文中进行更改但未保存时，它对其所有后代都可见，祖先。
When a change is made in a context, but not saved, it is visible to all of its’ descendants but not to its’ ancestors.
..它被推送到持久存储（通过持久存储协调器），并且对连接到存储的所有上下文都可见。
.. it is pushed to the persistent store (via the persistent store coordinator) and becomes visible to all contexts connected to the store.
推荐答案
我强烈建议避免父子环境设置。我们的书详细介绍了为什么它们常常导致奇怪的行为： https://www.objc.io / books / core-data /
I strongly recommend avoiding parent-child context setups. Our book goes into detail why they often lead to strange behaviour: https://www.objc.io/books/core-data/
短篇小说：他们并不像你认为的那样独立。
Short story: They're not as independent as you might think.
如果您需要多个单一上下文，请使用共享一个持久性存储协调器的多个上下文。
Use multiple context that share a single persistent store coordinator if you need more than a single context.
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