title: How to use birthday field in symfony2 forms
body: <p><a href="http://symfony.com/doc/current/reference/forms/types/birthday.html" rel="nofollow">Symfony Docs</a> say that we can use birthday date in forms. but they have not given any example how to use that</p>
  
  <p>Can anyone please tell me where do I need to write <code>birthday</code> in doctrine entity?</p>