title: How to validate a property dependent on another property in Symfony 2
body: <p>Is it possible to validate a property of a model class dependent on another property of the same class?</p>
  
  <p>For example, I have this class:</p>
  
  <pre><code>class Conference
  {
      /** $startDate datetime */
      protected $startDate;
  
      /** $endDate datetime */
      protected $endDate;
  }
  </code></pre>
  
  <p>and I want that Symfony 2.0 validates, that <code>$startDate</code> has to be after <code>$endDate</code>.</p>
  
  <p>Is this possible by annotations or do I have to do this manually?</p>