Singleton Entity in CoreData

Question

I might have my terminology incorrect in the title using the word singleton. I searching for a good technique now. I have an entity named user that stores a users logged in data such as a session key for making server requests. I only ever want one of these entities to exist ever. Is there a standard technique for doing this?

What I have so far is something like this

NSManagedObjectContext *moc = [self managedObjectContext];
    NSEntityDescription *entityDescription = [NSEntityDescription
                                              entityForName:@"UserEntity" inManagedObjectContext:moc];
    NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
    [request setEntity:entityDescription];


NSArray *array = [moc executeFetchRequest:request error:&error];
    if (array == nil)
    {
        // Deal with error...
    }

    if ([array count]==0) {
         //first run of app

    }else if([array count]==1)
    {
        // id like the code to enter here after every app run except for the first one

    }else
    {

        //dont want this to happen
    }

Answer 1

I use Matt Gallagher's approach described in his article Singletons, AppDelegates and top-level data.

It uses a macro to create a "synthesized singleton" class that you can then access from anywhere. Very handy for things like sessions, managed object contexts, etc. Otherwise you'd have to pass these round everywhere.

Answer 2

Your approach should work and it has the benefit of being flexible. Consider the possibility that a future version of your app has the ability to manage multiple accounts; you could easily achieve this if you model your "singleton" as a regular entity.

If you're 100% certain that you'd never want that, you could use the persistent store's metadata property for things like this.