title: NHibernate, ORM : how is refactoring handled? existing data?
body: <p>When using an ORM (specifically NHibernate), how is refactoring of data handled? I mean, if data objects change such that the underlying relational DB schema changes, does the ORM offer any help in schema upgrades / downgrades in the DB? How about migration of existing data to the new schema?</p>
  
  <p>I am in the process of making a decision on using an ORM and have very limited exposure. Please bear with me if the questions are naive.</p>