title: JMS Serializer: How to set auto_increment value in serialize
body: <p>I have a class which I want to serialize into a xml-object.
  My class has an "id" value and I need to set this. So the first has id=1, the second id=2 etc...
  Is it possible to set something in my Class that there is an auto_increment for each generatetd class?
  THANKS!!!</p>