keeping track of accessed objects in CoreData via objectID?

Question

I want to have table in CoreData that holds a list of other CoreData objects I have accessed, for instance I have Clients and I want a table RecentClients that is simply holding this list and the date they were accessed.

Can I store the objectID and then do a fetch request based on that?

EDIT: See Ben's answer below and then go here: http://cocoawithlove.com/2008/08/safely-fetching-nsmanagedobject-by-uri.html

Answer 1

You could just create the RecentClients as another entity in your Core Data model. It would then have a one to many relationship with the Client entity.

Answer 2

You'll want to convert the NSManagedObjectID to a string by calling its -URIRepresentation method. You can then convert the string back to an NSManagedObjectID using NSPersistentStore's -managedObjectIDForURIRepresentation: method.

If you store the strings, you should be able to do what you're describing, though you won't use a fetch request; you'll use -[NSManagedObjectContext objectWithID:]

Answer 3

How are you planning on storing the access date? If you make it an attribute of your Client entity, you can bump it each time the object is accessed and then use an NSFetchedResultsController that fetches Clients ordered by the access date. The downside is, of course, that you're modifying the instance every time you access it, which may not be ideal.