call method from NSManagedObject from uiviewController (MVC pattern) - objective-c

Question

My question is simple. How to communicate between my model and my controller ?
Code into controller
NSEntityDescription *entity = [NSEntityDescription entityForName:#"Album" inManagedObjectContext:manageContext];
album = [[Album alloc] initWithEntity:entity insertIntoManagedObjectContext:manageContext];
NSArray *arrayListAlbums = [album returnAllAlbums];
Method into NSManagedObject
(NSArray *) returnAllAlbums
{
NSEntityDescription *entitydescription = [NSEntityDescription entityForName:#"Album" inManagedObjectContext:managedObjContextAlbum];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entitydescription];
NSError *error;
NSArray *arrayListAlbums = [managedObjContextAlbum executeFetchRequest:request error:&error];
return arrayListAlbums;
}

Answer 1

From the code you provided, you have added a convenience method in your NSManagedObject subclass and then you create an instance of the NSManagedObject to call that convenience method. This is not a good design.
You are creating an empty data object to call a fetch method. Perhaps you should have a class method "somewhere" that looks like this:
+ (NSArray *)returnAllAlbums:(NSManagedObjectContext*)moc
{
NSEntityDescription *entitydescription = [NSEntityDescription entityForName:#"Album" inManagedObjectContext:moc];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entitydescription];
NSError *error;
NSArray *arrayListAlbums = [managedObjContextAlbum executeFetchRequest:request error:&error];
if (arrayListAlbums == nil) {
NSLog(#"Failed to fetch: %#\n%#", [error localizedDescription], [error userInfo]);
}
return arrayListAlbums;
}
Which you can then access without creating an empty data object:
NSArray *arrayListAlbums = [MyClassWithFetchMethods returnAllAlbums:myLocalContextReference];