如何跟踪/观察子图中的所有变化?

I have a NSManagedObjectContext in which I have a number of subclasses of NSManagedObjects such that some are containers for others. What I'd like to do is watch a top-level object to be notified of any changes to any of its properties, associations, or the properties/associations of any of the objects it contains.I have a NSManagedObjectContext in which I have