将一个实体的NSManagedObjectID保存为另一实体的属性？ [英] Saving the NSManagedObjectID from one entity as a property on a different Entity?

问题描述

我有一个核心数据实体，需要保留其他某些实体的 NSManagedObjectID 。为此，我正在考虑将ObjectID转换为字符串，该字符串是 NSManagedObject 属性的批准类型。

我可以从文档中读取到我可以通过以下方式获取ID的URI表示形式：

  NSURL * uriID = [[myEntity objectID ] URIRepresentation]; 
  

然后我可以通过以下方式将此URL转换为NSString：

  NSString * stringID = [uriID absoluteString]; 
  

这可以坚持到我的 NSManagedObject ' s NSString属性。

现在当我需要换行时会发生什么？

我想能够执行以下操作：

  if（[myManagedObject objectID] == value）
  

其中， 值 是 NSManagedObjectID 我早些时候转换为NSString。

要进一步说明原因：我需要能够保留Entity对象并保持另一个实体对象的ObjectID，以便我以后可以使用：这个对象的上一次交互是与此实体。

希望有人可以帮助我使它正常工作：）
谢谢

解决方案

为什么不只是在 Object 称为 interaction ，它指向 Entity 的实例，反之诗篇中，从 Entity 到 Object 的一对多关系称为 interactions ？

这可以很好地解决问题。

但是您也可以看看 code> 和 + URLWithString： 方法可用于其他方向。

I have a Core Data Entity that needs to hold onto the NSManagedObjectID of some other Entity. To do so I was considering converting the ObjectID to a string that is an approved type of an NSManagedObject attribute.

I can read from the documentation that I can get a URI representation of the ID by:

NSURL *uriID = [[myEntity objectID] URIRepresentation];

I can then convert this URL to an NSString by:

NSString *stringID = [uriID absoluteString];

This I can persist to my NSManagedObject's NSString attribute.

Now what happens when I need to go the other way?

I would like to be able to do something like this:

if([myManagedObject objectID] == value) 

where value is the NSManagedObjectID that I converted to an NSString earlier.

To shed a little more light on the why: I need to be able to have an Entity object hold and persist the ObjectID of another Entity object, so that I later on can go: this Objects last "interaction" was with this Entity.

Hope someone can help me get this working:) Thank you

解决方案

Why not just establish a to-one relationship property in Object called interaction, which points to an instance of an Entity — and vice verse, a to-many relationship from Entity to Object called interactions? This solves the problem pretty neatly, without all the conversion methods.

But you might also look at the -managedObjectIDForURIRepresentation: and +URLWithString: methods to go the other direction.

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