Pass custom product meta data to the order in Woocommerce 3

Question

In Woocommerce, I\'m attempting to add a piece of custom meta to my products and I would like to pass it through to orders.

We have a substantial amount of products and

Answer 1

I have revisited a bit your code. The following will save your product custom field "Cost centre" as hidden order item meta data, visible only in Admin Order edit pages on each item:

// Admin products: Display custom Field
add_action( 'woocommerce_product_options_general_product_data', 'product_options_general_product_data_add_field' );
function product_options_general_product_data_add_field() {
    global $post;

    echo '<div class="options_group">';

    woocommerce_wp_select( array(
        'id'      => '_cost_centre',
        'label'   => __( 'Cost Centre', 'woocommerce' ),
        'options' => array(
            'MFEG'   => __( 'MFEG', 'woocommerce' ), // Default displayed option value
            'YDIT'   => __( 'YDIT', 'woocommerce' ),
        )
    ) );

    echo '</div>';
}

// Admin products: Save custom Field
add_action( 'woocommerce_process_product_meta', 'product_options_general_product_data_save_field' );
function product_options_general_product_data_save_field( $post_id ){
    if( isset( $_POST['_cost_centre'] ) )
        update_post_meta( $post_id, '_cost_centre', esc_attr( $_POST['_cost_centre'] ) );
}

// Order items: Save product "Cost centre" as hidden order item meta data
add_action('woocommerce_checkout_create_order_line_item', 'save_file_type_as_order_item_meta', 20, 4);
function save_file_type_as_order_item_meta($item, $cart_item_key, $values, $order) {
    if ( $cost_centre = $values['data']->get_meta('_cost_centre') ) {
        $item->update_meta_data( '_cost_centre', $cost_centre ); // Save as order item (visble on admin only)
    }
}

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

Export: (In StackOverFlow, the rule is one question for one answer).

The WordPress/Woocommerce basic order export don't allow to export order items

You will need to use a third party plugin and depending on the chosen plugin, you will have to add your order item custom field _cost_centre for your export based on the plugin possibilities.