title: how to update yml created entities, if they are expanded with business logic?
body: <p>when you execute doctrine:generate:entities with a set of yml files containing your relation mapping, all Entity classes are automatically generated.</p>
  
  <p>When you adjust your yml files and regenerate the Entity classes, they are overwritten (and the old ones are backed up).</p>
  
  <p>In doctrine1, the entity-generator created Base Classes that where automatically inherited by the actual Entity Class, that you could expand with your own business logic.</p>
  
  <p>In doctrine2 I don't see those base classes, and I don't want to adjust my generated classes, because i won't be able to update my datamodel in my yml files.</p>
  
  <p>What is the Doctrine2 approach?
  Should i manually inherit from my generated Entity Classes to add business logic?
  Can doctrine adjust the Entity class, and keeping the additional changes (with some sort of diffing algorithm)?
  Does the entity-generation only be used once to generate the classes, and should all the datamodel changes be implemented manually in the Class itself?</p>