Small drop-in plugin to fix double-serialized product attributes (they are no longer double-unserialized in WC Core)

double-serialized-attributes-fixer.php

<?php
/**
 * Plugin Name: Double serialized attributes fixer
 * Description: Adds a tool to fix double serialized attributes in WooCommerce.
 * Version: 0.0.9
 * Author: Mike J
 * Requires at least: 4.4
 * Tested up to: 4.7
 */
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

add_filter( 'woocommerce_debug_tools', 'double_serialized_attributes_fixer_tool' );

function double_serialized_attributes_fixer_tool( $tools ) {
	$tools[ 'double_serialized_attributes_fixer' ]  = array(
		'name'     => 'Double-serialized attributes',
		'button'   => 'Fix double-serialized attributes',
		'desc'     => 'This tool will attept to fix all double-serialized attributes for products.',
		'callback' => 'double_serialized_attributes_fixer',
	);
	return $tools;
}

// Fixes double-serialised values - #14824.
function double_serialized_attributes_fixer() {
	global $wpdb;

	$product_ids = wp_parse_id_list( $wpdb->get_col( "SELECT ID FROM {$wpdb->posts} WHERE post_type = 'product';" ) );

	foreach ( $product_ids as $product_id ) {
		$attributes = get_post_meta( $product_id, '_product_attributes', true );

		if ( is_serialized( $attributes ) ) {
			$attributes = maybe_unserialize( $attributes );
			update_post_meta( $product_id, '_product_attributes', $attributes );
		}
	}
}