title: JPA EntityManager: why merge() method returns managed entity?
body: <p>Working of <code>merge()</code> method:</p>
  
  <blockquote>
    <p>The merge(source entity) method is going to copy the detached entity state (source) to a managed entity instance (destination). If the merging entity has no equivalent in the current Session, one will be fetched from the database. The detached object instance will continue to remain detached even after the merge operation.</p>
  </blockquote>
  
  <p>My question is:</p>
  
  <p>Why <code>merge()</code> method copy the detached entity state to managed entity and not just pass the same detached entity to the persistence context?</p>