schema.org book for WooCommerce

gistfile1.txt

<?php

// define the woocommerce_structured_data_product callback
function filter_woocommerce_structured_data_product( $markup, $product ) {
    $formaat = get_field("boek_formaat");
    $authors = get_field("boek_auteurs");
    $date = get_the_date('Y m d');
    $markup['additionalType'] = "book";
    $markup['brand'] = "Ertsberg";
	  $markup['isbn'] = $product->get_sku();
    $markup['author'] = ['@type' => 'Person', 'name' => $authors];
    $markup['datePublished'] = $date;
    $markup['inLanguage'] = "nl-BE";
    $markup['copyrightHolder'] = ['@type' => 'Organisation', 'name' => 'Erstberg'];
    $markup['publisher'] = ['@type' => 'Organisation', 'name' => 'Erstberg'];
    $markup['bookFormat'] = $formaat;
    return $markup;
};

// add the filter
add_filter( 'woocommerce_structured_data_product', 'filter_woocommerce_structured_data_product', 10, 2 );

?>