Change user role after purchase

gistfile1.txt

// If customer purchases a special product, change user role to allow access to that product
// Make sure to add corresponding value to product's custom field "new_role"

add_action( 'woocommerce_order_status_completed', 'change_role_on_purchase' );
function change_role_on_purchase( $order_id ) {
    $order = wc_get_order( $order_id );
    $items = $order->get_items();

    foreach ( $items as $item ) {
        $product_id = $item->get_product_id();
        $new_role = get_post_meta( $product_id, 'new_role', true );

        if ( $order->user_id > 0 && (!empty($new_role)) ) {
            $user = new WP_User( $order->user_id );

            // Change role
            $user->remove_role( 'customer' );
            $user->add_role( $new_role );

            // Exit the loop
            break;
        }
    }
}