Woocommerce Produkt Variation - ein eigenes Feld einfügen

// Display Fields
add_action( 'woocommerce_product_after_variable_attributes', 'variable_fields', 10, 2 );
//JS to add fields for new variations
add_action( 'woocommerce_product_after_variable_attributes_js', 'variable_fields_js' );
//Save variation fields
add_action( 'woocommerce_process_product_meta_variable', 'variable_fields_process', 10, 1 );
function variable_fields( $loop, $variation_data ) { ?>
    <tr>
        <td>
            <div>
                    <label></label>
                    <input type="text" size="5" name="my_custom_field[]" value=""/>
            </div>
        </td>
    </tr>
<tr>
        <td>
            <div>
                    <label></label>
            </div>
        </td>
    </tr>
<?php }
function variable_fields_process( $post_id ) {
    if (isset( $_POST['variable_sku'] ) ) :
        $variable_sku = $_POST['variable_sku'];
        $variable_post_id = $_POST['variable_post_id'];
        $variable_custom_field = $_POST['my_custom_field'];
        for ( $i = 0; $i < sizeof( $variable_sku ); $i++ ) :
            $variation_id = (int) $variable_post_id[$i];
            if ( isset( $variable_custom_field[$i] ) ) {
                update_post_meta( $variation_id, '_my_custom_field', stripslashes( $variable_custom_field[$i] ) );
            }
        endfor;
    endif;
}