title: How can I track/observe all changes within a subgraph?
body: <p>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.</p>
  
  <p>Using the context's 'hasChanges' doesn't give me enough granularity.  The objects 'isUpdated' method only applies to the given object (and not anything in its associations).  Is there a convenient (perhaps, KVO-based) was I can observe changes in a context that are limited to a subgraph?</p>