WordPress Example Plugin: Comment meta data test

commentmeta-single.php

<?php
/*
  Plugin Name: Comment meta data test
  Version: 1.0
  Plugin URI: http://wpengineer.com
  Description: Comment meta data test
  Author: Latz
  Author URI: http://wpengineer.com
 */


add_filter( 'comment_form_defaults',	'change_comment_form_defaults');

function change_comment_form_defaults($default) {

	$commenter = wp_get_current_commenter();	

		$default['fields']['email'] .= '<p class="comment-form-author">' .
						'<label for="city">'. __('City') . '</label>
						<span class="required">*</span>
		        <input id="city" name="city" size="30" type="text" /></p>';
	
	return $default;
}


add_filter( 'preprocess_comment', 'verify_comment_meta_data' );
function verify_comment_meta_data($commentdata) {
  if ( ! isset( $_POST['city'] ) )
        wp_die( __('Error: please fill the required field (city).') );
		return $commentdata;
}


add_action( 'comment_post',	'save_comment_meta_data' );
function save_comment_meta_data( $comment_id ) {
	add_comment_meta( $comment_id, 'city', $_POST['city'] );
}


add_filter( 'get_comment_author_link',	'attach_city_to_author' );
function attach_city_to_author( $author ) {
  $city = get_comment_meta( get_comment_ID(), 'city', true );
  if ( $city )
    $author .= " ($city)";
	return $author;
}


?>