Add a custom multi-select field to admin product options settings in Woocommerce

Question

I have followed this answer How to add more custom field in Linked Product of Woocommerce to add a custom select field to my Linked Product screen in Woocommerce. This new field

Answer 1

This kind of select field only works with a defined multiple attribute and work with an array of values. so you can't use it for a simple ID. If you add to your select field multiple="multiple" attribute it will work.

Also since Woocommerce 3 things have changed:
- There are better hooks to save the data.
- You can now use CRUD Objects and related methods.

The following code will work for multiple product IDs (an array of products IDs):

// Display a custom select field in "Linked Products" section
add_action( 'woocommerce_product_options_related', 'display_linked_products_data_custom_field' );
function display_linked_products_data_custom_field() {
    global $product_object, $post;
    ?>
    

        
        
            get_meta( '_subscription_toggle_ids' );

                foreach ( $product_ids as $product_id ) {
                    $product = wc_get_product( $product_id );
                    if ( is_object( $product ) ) {
                        echo '' . wp_kses_post( $product->get_formatted_name() ) . '';
                    }
                }
            ?>
        
    
    update_meta_data( '_subscription_toggle_ids', $data );
}

Code goes in function.php file of your active child theme (active theme). Tested and works.