public static function addFav($drink)
 {
     $user = $_SESSION['user'];
     $errors = Drink::validateFavoriteDoesntExist($user, $drink);
     if (count($errors) > 0) {
         Redirect::to('/drink', array('message' => $errors[0]));
     }
     Drink::addFavorite($user, $drink);
     Redirect::to('/drink', array('message' => 'Favorite has been added.'));
 }