title: Trigger Hibernate(pre/post)Update Event when Relationship Changes
body: <p>I have implemented the pre/post event listeners for Hibernate events with one caveat I haven't been able to overcome. I have a <code>Departments</code> entity that has a many-to-many relationship back to a <code>Centers</code> entity. When assigning a new Center to a Department, I simply invoke:</p>
  
  <pre><code>oDepartment.addCenter(oCenter);
  entitySave(oDepartment);
  </code></pre>
  
  <p>When this happens, I would expect Hibernate to trigger the preUpdate and postUpdate events since I modified the entity. However, it's never triggered unless a column property is also updated. Updating only a relationship property does not seem to trigger the update events.</p>
  
  <p>Looking through the current Hibernate session, I can't seem to find anything that would allow me to set some sort of flag that would trigger these events to fire.</p>
  
  <p>Thoughts on a way I could get these events to fire?</p>