class-tiny-migration.php

<?php
/*
* Tiny Compress Images - WordPress plugin.
* Copyright (C) 2015-2018 Tinify B.V.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc., 51
* Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

class Tiny_Migration {

    public static function migrate_meta_key_on_update() {
        $saved_version = get_option('tiny_png_plugin_version');

        if ($saved_version !== TINY_PNG_PLUGIN_VERSION) {
            global $wpdb;

            $posts = $wpdb->get_results("
                SELECT post_id, meta_value 
                FROM {$wpdb->postmeta} 
                WHERE meta_key = 'tiny_compress_images'
            ");

            foreach ($posts as $post) {
                update_post_meta($post->post_id, Tiny_Config::META_KEY, $post->meta_value);

                delete_post_meta($post->post_id, 'tiny_compress_images');
            }

            update_option('tiny_png_plugin_version', TINY_PNG_PLUGIN_VERSION);
        }
    }
}

add_action('plugins_loaded', array('Tiny_Migration', 'migrate_meta_key_on_update'));