/** 
  * Attaches karam to a user
  * @param int $user_id
  * @param int $karma_id
  * @return bool
  */
 public static function attachKarma($user_id, $karma_id)
 {
     $karma = new KarmaUser();
     $karma->user_id = $user_id;
     $karma->karma_id = $karma_id;
     if ($karma->validate()) {
         $karma->save();
         return true;
     } else {
         return false;
     }
 }