title: Creating portable Bundles with extendable entities in Symfony2
body: <p>I want to create some Symfony2 bundles which are reusable accross different projects, but where the entities also can be easily extended if required.</p>
  
  <p>An example could be a reusable UserBundle, which contains a User entity with all the ORM mappings defined. In my application however, I might want to extend this entity and add extra columns, associations or override some of the parent's mappings.</p>
  
  <p>The closest solution I could find are Doctrine2's mapped superclasses, but then I'd lose the plug-and-playness of my reusable bundle, I'd always have to extend the mapped superclass in my application even if I don't wish to modify the mappings.</p>
  
  <p>The other documented inheritance schemes require modifying the parent's mappings, and then my UserBundle wouldn't be portable anymore accross projects.</p>
  
  <p>Is there a way to define a fully-working entity in one bundle, and still extend that in another bundle?</p>