Migrating from string to integer primary keys in CakePHP

migration.php

<?php
App::uses('AppShell', 'Console/Command');
class UserIdFromVarcharToInt extends CakeMigration {

    public $description = '';

    public $migration = array(
        'up' => array(
            'alter_field' => array(
                'users' => array(
                  'id' => array('type' => 'integer', 'null' => false, 'default' => NULL, 'length' => 10, 'key' => 'primary', 'collate' => null, 'charset' => null),
                ),
            ),
        ),
        'down' => array(
            'alter_field' => array(
                'users' => array(
                    'id' => array('type' => 'string', 'null' => false, 'default' => NULL, 'length' => 36, 'key' => 'primary', 'collate' => 'utf8_general_ci', 'charset' => 'utf8'),
                ),
            ),
        ),
    );

    public function before($direction) {
        if ($direction != 'up') {
            return true;
        }

        $this->AppShell = new AppShell(); // For console output

        $this->User = ClassRegistry::init('AppUser');

        $users = $this->User->find('all', array('fields' => 'id'));
        if (empty($users)) {
            return true;
        }

        $count = 1;
        foreach($users as $user) {
            $id = $user['AppUser']['id'];

            $query = sprintf('UPDATE `users` SET `id` = %d WHERE `id` = \'%s\' LIMIT 1', $count, $id);
            $this->User->query($query);
            $this->AppShell->out($query);
            $this->AppShell->out('User "' . $id  . '" has a new primary key of: ' . $count);

            $count++;
        }
        return true;
    }

    public function after($direction) {
        return true;
    }
}