title: Hibernate is *NOT* throwing an exception (I think it should)
body: <p>The Hibernate JavaDoc states that <code>Session.update(Object o)</code> would raise an exception if there's already a persistent instance of <code>o</code>, right?</p>
  
  <pre>If there is a persistent instance with the same identifier, an exception is thrown.</pre>
  
  <p>However, the following code doesn't throw anything when I run it. And I think it should!</p>
  
  <pre><code>Email email = new Email("andre", "girafa", "hi");
  
  Session session = factory.openSession();
  Transaction tx = session.beginTransaction();
  
  session.save(email);
  session.update(email);
  session.update(email);
  
  tx.commit();
  
  // didn't throw... Let's try again
  
  tx = session.beginTransaction();
  
  session.update(email);
  session.update(email);
  
  tx.commit();
  session.close();
  
  // still nothing! :(
  </code></pre>
  
  <p>As you can say, <strong>twice</strong> I try to do multiple <code>update()</code>s, but still Hibernate's taking easy on me.</p>
  
  <p>Anybody has a hunch why?</p>
  
  <p><strong>EDIT:</strong> it seems that it would only throw if <em>another equivalent object</em>, for instance, <code>email2</code> with the same ID as <code>email</code>. I guess the documentation was kinda sloppy there.</p>