Hello. I have a Core Data model, and was wondering if you know how to create a binding to an Entity, programmatically? Normally you use bind:toObject:withKeyPath:options: to create a binding. But I'm having a little difficulty getting this to work with Core Data, and couldn't find anything in Apple's docs regarding doing this programmatically.

The Core Data model is simple:

• An Entity called Book
• An Attribute of Book called author (NSString)

I have an object called BookController. It looks like so:

@interface BookController : NSObject
{
    NSString *anAuthor;
}

@property (nonatomic, retain) NSString *anAuthor;  // @synthesize anAuthor; inside @implementation

I'd like to bind anAuthor inside BookController, to author inside a Book entity. This is how I'm attempting to wrongly do it (it partially works):

// A custom class I made, providing an interface to the Core Data database
CoreData *db = [[CoreData alloc] init];

// Creating a Book entity, saving it
[db addMocObject:@"Book"];
[db saveMoc];

// Fetching the Book entity we just created
NSArray *books = [db fetchObjectsForEntity:@"Book" withPredicate:nil withSortDescriptors:nil];
NSManagedObject *book = [books objectAtIndex:0];

// Creating the binding
BookController *bookController = [[BookController alloc] init];
[bookController bind:@"anAuthor" toObject:book withKeyPath:@"author" options:nil];

// Manipulating the binding
[bookController setAnAuthor:@"Bill Gates"];

Now, when updating from the perspective of bookController, things don't work quite right:

// Testing the binding from the bookController's perspective
[bookController setAnAuthor:@"Bill Gates"];

// Prints:  "bookController's anAuthor: Bill Gates"
NSLog(@"bookController's anAuthor: %@", [bookController anAuthor]);     // OK!

// ERROR HERE - Prints:  "bookController's anAuthor: (null)"
NSLog(@"Book's author: %@", [book valueForKey:@"author"]);              // DOES NOT WORK!  :(

When updating from the perspective of the Book entity, things work fine:

// ------------------------------
// Testing the binding from the Book's (Entity) perspective (this works perfect)
[book setValue:@"Steve Jobs" forKey:@"author"];

// Prints:  "bookController's anAuthor: Steve Jobs"
NSLog(@"bookController's anAuthor: %@", [bookController anAuthor]);     // OK!

// Prints:  "bookController's anAuthor: Steve Jobs"
NSLog(@"Book's author: %@", [book valueForKey:@"author"]);              // OK!

It appears that the binding is partially working. I can update it on the side of the Model and it propagates up to the Controller via KVO, but if I update it on the side of the Controller, it doesn't trickle down to the Model via KVC.

Any idea on what I'm doing wrong? Thanks so much for looking! :)