Creating a unique id for a Core Data program on the iPhone

Question

I am having a bit of trouble figuring out this Core Data stuff. How do I create a new entry with a unique ID? In SQL I would just declare one field as an autoincrement fie

Answer 1

Here are three kinds of unique ID representation of CoreData object:

NSManagedObjectID *taskID = [task objectID];
NSURL *taskUniqueURLKey = task.objectID.URIRepresentation;
NSString *taskUniqueStringKey = task.objectID.URIRepresentation.absoluteString;

!!!!Note: if you want to use above unique key as index, please make sure the object is saved to context before using it , or the objectID would be a temporary Id, which will be replaced later (e.g. after saved). See the apple document of NSManagedObjectID class :

- (BOOL)isTemporaryID;    // indicates whether or not this ID will be replaced later, 
such as after a save operation (temporary IDs are assigned to newly inserted objects 
and replaced with permanent IDs when an object is written to a persistent store); most
 IDs return NO