title: Hibernate updates child entity with null and not removes, how to force it?
body: <p>
  I have Playlist entity that owns collection of clips annotated with CascadeType.All. Although, in fact, it is bidirectional relationship, I defined it unidirectional to avoid exccessive cascades. So Clip has playlistId integer property and not reference to playlist. Clip is defined as part of playlist, so it can't exist without it. Therefore 'Playlist_ID' column in DB is defined not-null and getPlayListId() too. I read, that if I remove item from collection, cascade considers it as remove of relationship, but not entity removal. In my case it is a problem, since cascade tries to set Playlist_ID column to null and causes constraint violation. 
  </p>
  <p>I want the code: <br/>
  playlist.getClips().remove(0); dao.update(playlist)
  <br/>will delete the clip. Is there any way to do it?</p>