WooCommerce: Adding custom fields to checkout, order/user meta and emails

woocommerce_custom_checkout_fields.php

<?php
/** ###################################################### *
 *                                                         *
 * Adding custom fields to checkout, order/user meta and emails *
 *                                                         *
 * ####################################################### */

/**
 * Add the 'Profissão' field to the checkout
 **/
add_action('woocommerce_after_order_notes', 'billing_position_field');

function billing_position_field( $checkout ) {

    echo '<div id="billing_position_field">';

    woocommerce_form_field( 'billing_position', array(
        'type'          => 'text',
        'class'         => array('form-row-wide'),
        'label'         => __('Profiss&atilde;o'),
        'placeholder'   => __('Profiss&atilde;o'),
        ), $checkout->get_value( 'billing_position' ));

    echo '</div>';

    echo '<script type="text/javascript">jQuery(document).ready(function() { jQuery("#billing_position_field").detach().insertAfter("#billing_cnpj_field"); });</script>';

}

/**
 * Process the checkout
 **/
add_action('woocommerce_checkout_process', 'billing_position_field_process');

function billing_position_field_process() {
    global $woocommerce;

    // Check if set, if its not set add an error. This one is only requite for companies
    if ($_POST['billing_company'])
        if (!$_POST['billing_position'])
            $woocommerce->add_error( __('Por favor, digite sua profiss&atilde;o.') );
}

/**
 * Update the user meta with field value
 **/
add_action('woocommerce_checkout_update_user_meta', 'billing_position_field_update_user_meta');

function billing_position_field_update_user_meta( $user_id ) {
    if ($user_id && $_POST['billing_position']) update_user_meta( $user_id, 'billing_position', esc_attr($_POST['billing_position']) );
}

/**
 * Update the order meta with field value
 **/
add_action('woocommerce_checkout_update_order_meta', 'billing_position_field_update_order_meta');

function billing_position_field_update_order_meta( $order_id ) {
    if ($_POST['billing_position']) update_post_meta( $order_id, 'Profiss&atilde;o', esc_attr($_POST['billing_position']));
}

/**
 * Add the field to order emails
 **/
add_filter('woocommerce_email_order_meta_keys', 'billing_position_field_order_meta_keys');

function billing_position_field_order_meta_keys( $keys ) {
    $keys[] = 'Profiss&atilde;o';
    return $keys;
}
?>