For to-many relationships, KVC compliance requires that:
- Your class implements a method named -<key> that returns an array, has an array instance variable named <key> or _<key>, or implements the methods -countOf<Key> and -objectIn<Key>AtIndex:. Optionally, you can also implement -get<Key>:range: to improve performance.
- If the to-many related objects are mutable, and the -<key> method does not return an NSMutableArray, you must also implement -insertObject:in<Key>AtIndex: and -removeObjectFrom<Key>AtIndex:. Optionally, you can also implement -replaceObjectIn<Key>AtIndex:withObject: to improve performance.