NSPredicate Query

[Martyn]

Good evening Sirs,

I am having a little trouble performing a 'query' using NSPredicate on two entities in my Core Data project.

The two entities are:

Author {authorName, dateOfBirth}
Book {authorName, bookName, pages}

I have setup the relationships correctly (one author has many books, inverse).

At the moment I can click on an author in a view controller, and it will take me to a detail view controller that will display all books by all authors. I would much rather the detail view controller displayed all the books by a certain author (the one that is clicked in the view controller).

I presume I need to do a NSPredicate Query to achieve this? So far I have:

	// Gets new name of author.
	NSManagedObject *selectedObject = [[self fetchedResultsController] objectAtIndexPath:indexPath];
	NSString *newAuthorName = [[selectedObject valueForKey:@"authorName"] description];
	
	// Begin predicate query.
	NSFetchRequest *myFetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Books" inManagedObjectContext:managedObjectContext_];
    [myFetchRequest setEntity:entity];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%@==%@", newAuthorName, authorName];
    [myFetchRequest setPredicate:predicate];
    NSError *error;
	NSArray *listArray;
    listArray = [[managedObjectContext_ executeFetchRequest:myFetchRequest error:&error] mutableCopy];
	NSLog(@"listArray: %@", listArray);

I would expect that this would return all the books by a certain author (the relevant author name is passed into the detail view controller from the prior view controller).

However, I am not sure I am using the correct code for the predicate as they are my weakness.

Also, I am a little unsure what to do with the returned 'listArray'.

I would be very grateful if anyone could help me out here. I think I have explained the problem pretty well, but if more clarity is needed just ask

[Martyn]

A gentle bump for a stuck man.

[Martyn]

...

[Martyn]

...