Woocommerce - Filter orders in wp-admin by products

gistfile1.php

/***********************************************************************************
 *  2. FILTRO POR PRODUCTOS EN PEDIDOS
 ***********************************************************************************/

define('FILTRO_PRODUCT_NAME', 'filtro_producto');
define('ORDER_POST_TYPE', 'shop_order');

/**
 * Añade la query de las sedes 
 * Hook 'pre_get_posts'
 * @global type $pagenow
 * @global type $typenow
 * @param type $query
 */
function query_filter_product_order( $query ){
    global $pagenow, $typenow;

    if ( $query->is_main_query() && is_admin() && $pagenow=='edit.php' && $typenow == ORDER_POST_TYPE && isset($_GET[FILTRO_PRODUCT_NAME])) {
        
        global $wpdb;
        $wpdb->show_errors;
        
        $producto_id = $_GET[FILTRO_PRODUCT_NAME];
        
        // 1. Sacamos los "order_items" que tienen nuestro producto
        $order_items = $wpdb->get_col( $wpdb->prepare("SELECT order_item_id FROM wp_woocommerce_order_itemmeta WHERE meta_key = '_product_id' AND meta_value= %d", $producto_id) );
        
        if (empty($order_items))
            return $query;
        
        // 2. Sacamos los orders de los $order_items
        $orders = $wpdb->get_col( $wpdb->prepare("SELECT order_id FROM wp_woocommerce_order_items WHERE order_item_id IN (%s)", implode($order_items)) );
        
        if (empty($orders))
            return $query;
        
        
        $query->set('post__in', $orders);
    }
} add_filter( 'pre_get_posts', 'query_filter_product_order' );

/**
 * Hook que añade el select  de sedes a la zona de filtros de edit.php
 * Hook 'restrict_manage_posts'
 * @global type $typenow
 * @global type $wp_query
 * @return boolean
 */
function filter_product_order(){
    

    global $typenow;
    
    if ( $typenow != 'shop_order')
        return false;
    
    $productos = get_posts( array('post_type' =>'product', 'posts_per_page' => -1, 'orderby' => 'title', 'order' => 'ASC'));

    $selected = empty( $_REQUEST[FILTRO_PRODUCT_NAME] )?'':$_REQUEST[FILTRO_PRODUCT_NAME];
    
    if ( $productos ):
    ?>
    <select name="<?php echo FILTRO_PRODUCT_NAME ?>">
        <option value=""><?php _e('Filtrar por producto', 'instema')?></option>
        <?php foreach( $productos as $producto ): ?>
        <option <?php selected($selected, $producto->ID)?> value="<?php echo $producto->ID ?>"><?php echo $producto->post_title ?></option>
        <?php endforeach;?>
    </select>    
    <?php endif;
 
} add_action( 'restrict_manage_posts', 'filter_product_order' );