migration_script

<?php
/**
 * Revised version
 *
 * How to use:
 *   1. Place this script in WordPress root directory.
 *   2. Log in your WordPress admin dashborad.
 *   3. put the address of this file in the Browser's address bar:
 *      e.g. http://example.com/wordpress/this_file.php
 *   4. Wait until 'Finished!' message is shown.
 *
 * This script will take the more time if you have the more uploaded files.
 * So I recommend you to write the snippet below in your theme's functions.php
 *
 * function maintenace_mode() {
 * if (!current_user_can('manage_options') && !is_user_logged_in())
 *   wp_die('<h1>Maintenace Work in Progress</h1>');
 * }
 * add_action('get_header', 'maintenace_mode');
 *
 */
if (current_user_can('manage_options' && !is_user_logged_in())) die();

require_once('./wp-config.php');

global $wpdb;

// STAGE 1: to rewrite _wp_attached_file values in postmeta table
$key = '_wp_attached_file';

$wpdb->query("UPDATE $wpdb->postmeta SET meta_value=SUBSTRING(meta_value, 9) WHERE meta_key='{$key}'");

// STAGE 2: to rewrite guid value in posts table
//          and _wp_attachment_metadata in postmeta table at a time
$data = $wpdb->get_results("select ID, guid from $wpdb->posts WHERE post_type='attachment'");
foreach ($data as $d) {
    if (preg_match("/\\/wp-content\\/uploads\\/\\d{4}\\/\\d{2}\\/(.+)$/", $d->guid)) {
        $new_guid = preg_replace("/\\d{4}\\/\\d{2}\\//", '', $d->guid);
        $wpdb->query("UPDATE $wpdb->posts SET guid='{$new_guid}' WHERE ID='{$d->ID}'");
        $meta_data = get_metadata('post', $d->ID, '_wp_attachment_metadata', true);
        $unserialized_meta_data = maybe_unserialize($meta_data);
        $new_meta_data = preg_replace("/\\d{4}\\/\\d{2}\\//", '', $unserialized_meta_data['file']);
        $unserialized_meta_data['file'] = $new_meta_data;
        $serialized_meta_data = maybe_serialize($unserialized_meta_data);
        update_metadata('post', $d->ID, '_wp_attachment_metadata', $serialized_meta_data);
    }
}
echo 'Finished!';
?>