Add custom field to product inventory tab and display value on single product page where meta ends - wordpress

Question

I'm using the following code in my theme functions.php file to add a additional data field to the product inventory tab:
// Add Custom Field to woocommerce inventory tab for product
add_action('woocommerce_product_options_inventory_product_data', function() {
woocommerce_wp_text_input([
'id' => '_number_in_package',
'label' => __('Number of Pages', 'txtdomain'),
'type' => 'number',
]);
});
add_action('woocommerce_process_product_meta', function($post_id) {
$product = wc_get_product($post_id);
$num_package = isset($_POST['_number_in_package']) ? $_POST['_number_in_package'] : '';
$product->update_meta_data('_number_in_package', sanitize_text_field($num_package));
$product->save();
});
add_action('woocommerce_product_meta_start', function() {
global $post;
$product = wc_get_product($post->ID);
$num_package = $product->get_meta('_number_in_package');
if (!empty($num_package)) {
printf('<div class="custom-sku">%s: %s</div>', __('Number of Pages', 'txtdomain'), $num_package);
}
});
add_filter('woocommerce_product_data_tabs', function($tabs) {
$tabs['additional_info'] = [
'label' => __('Additional info', 'txtdomain'),
'target' => 'additional_product_data',
'class' => ['hide_if_external'],
'priority' => 25
];
return $tabs;
});
However, on the single product page, the custom field is added before category and ISBN. I want to place the custom field at the end after the product ISBN. Any advice?

Answer 1

Some comments/suggestions regarding your code attempt
To save fields you can use the woocommerce_admin_process_product_object hook, opposite the outdated woocommerce_process_product_meta hook
WooCommerce contains by default no ISBN field, but it looks like the woocommerce_product_meta_end hook will answer your question
So you get:
// Add custom field
function action_woocommerce_product_options_inventory_product_data() {
woocommerce_wp_text_input( array(
'id' => '_number_in_package',
'label' => __( 'Number of Pages', 'woocommerce' ),
'description' => __( 'This is a custom field, you can write here anything you want.', 'woocommerce' ),
'desc_tip' => 'true',
'type' => 'number'
) );
}
add_action( 'woocommerce_product_options_inventory_product_data', 'action_woocommerce_product_options_inventory_product_data' );
// Save custom field
function action_woocommerce_admin_process_product_object( $product ) {
// Isset
if ( isset( $_POST['_number_in_package'] ) ) {
// Update
$product->update_meta_data( '_number_in_package', sanitize_text_field( $_POST['_number_in_package'] ) );
}
}
add_action( 'woocommerce_admin_process_product_object', 'action_woocommerce_admin_process_product_object', 10, 1 );
// Display on single product page
function action_woocommerce_product_meta_end() {
global $product;
// Is a WC product
if ( is_a( $product, 'WC_Product' ) ) {
// Get meta
$number = $product->get_meta( '_number_in_package' );
// NOT empty
if ( ! empty ( $number ) ) {
echo '<p>' . $number . '</p>';
}
}
}
add_action( 'woocommerce_product_meta_end', 'action_woocommerce_product_meta_end', 10 );