The CoreData documentation says "You can sometimes benefit from creating your own unique ID (UUID) property which can be defined and set for newly inserted objects. This allows you to efficiently locate specific objects using predicates (though before a save operation new objects can be found only in their original context)."
What should be used for this type?
A managed object's objectID is usually 'NSManagedObjectID' type but the DataModel wizard tool via XCode that allows you to set the type for a given attribute only has the basic allowed types in addition to 'Undefined', Binary Data, & Transformable.
If I wanted to have an attribute that serves as a secondary id for an object (in addition to it's standard ObjectID), do you store it as an NSString or would you custom modify the object model to hold NSManagedObjectID?
(for iPhone app/CoreData development)