How to handle exceptions on Doctrine 2 validation

[conanl]

I'm new to Doctrine 2 (and exceptions in PHP, really), but am trying to come up with a robust validation engine on Doctrine 2 (on top of CodeIgniter), following this page.Right now I'm wondering where I would define the ValidateException class, and how to 'try' doing a save (persist?) on my entity (from a controller, library, etc).I'd like to have something where, after doing this (in an 'authentication' library, for example):\[code\]$user->username = $username;$user->email_address = $email_address;$user->password = $password;$em->persist($user);$em->flush();return $foo; //where $foo refers to whether $em->flush() worked...\[/code\]I could simply return whether that persistence was successful (i.e., passed validation and saved), or not successful (i.e., failed validation).