title: What's the difference between session.Merge and session.SaveOrUpdate?
body: <p>I notice sometimes with my parent/child objects or many-to-many relationships, I need to call either <code>SaveOrUpdate</code> or <code>Merge</code>. Usually, when I need to call <code>SaveOrUpdate</code>, the exception I get on calling <code>Merge</code> has to do with transient objects not being saved first.</p>
  
  <p>Please explain the difference between the two.</p>