title: GWT RequestFactory: how to handle entities with composite primary keys
body: <p>Can RequestFactory handle composite primary keys? </p>
  
  <p>The <a href="http://code.google.com/webtoolkit/doc/latest/DevGuideRequestFactory.html" rel="nofollow">documentation</a> mentions that entities must implement <code>getId()</code>; how should this be implemented in the case where entities do not have a single "id" field, but rather have multiple foreign key fields that together constitute a composite primary key?</p>