What is the difference between SaveOrUpdateCopy and SaveOrUpdate in Nhibernate?

What is the difference between SaveOrUpdateCopy and SaveOr开发者_如何学GoUpdate method in NHibernate?

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From nHibernate doc:

Copy the state of the given object onto the persistent object with the same identifier. If there is no persistent instance currently associated with the session, it will be loaded. Return the persistent instance. If the given instance is unsaved or does not exist in the database, save it and return it as a newly persistent instance. Otherwise, the given instance does not become associated with the session.

There is one nice blog post on the subject.