title: Django Model - Incrementing Version Number like Grails
body: <p>We are looking at moving from Grails to Django.. </p>
  
  <p>In Grails every Domain Class (Model in Django) has an Integer field called "version" when the Domain class is Updated it is incremented by 1. </p>
  
  <p>(Grails/Hibernate also use this field to check that the Row has not been updated by the user since the data was loaded. But that is another issue.)</p>
  
  <p>How can I add an Integer field called version which is incremented each time the model is Saved/Updated in the database?</p>