How to add custom fields to WordPress comments

comments-example.php

<?php
/*
Plugin Name: Add Extra Comment Fields
Plugin URI: http://pmg.co/category/wordpress
Description: An example of how to add, save and edit extra comment fields in WordPress
Version: n/a
Author: Christopher Davis
Author URI: http://pmg.co/people/chris
License: MIT
*/

/**
 * Add our field to the comment form
 */
add_action( 'comment_form_logged_in_after', 'pmg_comment_tut_fields' );
add_action( 'comment_form_after_fields', 'pmg_comment_tut_fields' );
function pmg_comment_tut_fields()
{
    ?>
    <p class="comment-form-title">
        <label for="pmg_comment_title"><?php _e( 'Title' ); ?></label>
        <input type="text" name="pmg_comment_title" id="pmg_comment_title" />
    </p>
    <?php
}

/**
 * Cheating.  Get everything to be styled nicely in Twenty Elevent
 */
add_action( 'wp_head', 'pmg_comment_tut_style_cheater' );
function pmg_comment_tut_style_cheater()
{
    ?>
    <style type="text/css">
        #respond .comment-form-title {
            position: relative;
        }
        #respond .comment-form-title label {
            background: #EEE;
            -webkit-box-shadow: 1px 2px 2px rgba(204,204,204,0.8);
            -moz-box-shadow: 1px 2px 2px rgba(204,204,204,0.8);
            box-shadow: 1px 2px 2px rgba(204,204,204,0.8);
            color: #555;
            display: inline-block;
            font-size: 13px;
            left: 4px;
            min-width: 60px;
            padding: 4px 10px;
            position: relative;
            top: 40px;
            z-index:1;
        }
    </style>
    <?php
}

/**
 * Add the title to our admin area, for editing, etc
 */
add_action( 'add_meta_boxes_comment', 'pmg_comment_tut_add_meta_box' );
function pmg_comment_tut_add_meta_box()
{
    add_meta_box( 'pmg-comment-title', __( 'Comment Title' ), 'pmg_comment_tut_meta_box_cb', 'comment', 'normal', 'high' );
}

function pmg_comment_tut_meta_box_cb( $comment )
{
    $title = get_comment_meta( $comment->comment_ID, 'pmg_comment_title', true );
    wp_nonce_field( 'pmg_comment_update', 'pmg_comment_update', false );
    ?>
    <p>
        <label for="pmg_comment_title"><?php _e( 'Comment Title' ); ?></label>
        <input type="text" name="pmg_comment_title" value="<?php echo esc_attr( $title ); ?>" class="widefat" />
    </p>
    <?php
}

/**
 * Save our comment (from the admin area)
 */
add_action( 'edit_comment', 'pmg_comment_tut_edit_comment' );
function pmg_comment_tut_edit_comment( $comment_id )
{
    if( ! isset( $_POST['pmg_comment_update'] ) || ! wp_verify_nonce( $_POST['pmg_comment_update'], 'pmg_comment_update' ) ) return;
    if( isset( $_POST['pmg_comment_title'] ) )
        update_comment_meta( $comment_id, 'pmg_comment_title', esc_attr( $_POST['pmg_comment_title'] ) );
}

/**
 * Save our title (from the front end)
 */
add_action( 'comment_post', 'pmg_comment_tut_insert_comment', 10, 1 );
function pmg_comment_tut_insert_comment( $comment_id )
{
    if( isset( $_POST['pmg_comment_title'] ) )
        update_comment_meta( $comment_id, 'pmg_comment_title', esc_attr( $_POST['pmg_comment_title'] ) );
}


/**
 * add our headline to the comment text
 * Hook in way late to avoid colliding with default
 * WordPress comment text filters
 */
add_filter( 'comment_text', 'pmg_comment_tut_add_title_to_text', 99, 2 );
function pmg_comment_tut_add_title_to_text( $text, $comment )
{
    if( is_admin() ) return $text;
    if( $title = get_comment_meta( $comment->comment_ID, 'pmg_comment_title', true ) )
    {
        $title = '<h3>' . esc_attr( $title ) . '</h3>';
        $text = $title . $text;
    }
    return $text;
}


// update 2012-09-12 to show how to put the title in the comments list table

add_action('load-edit-comments.php', 'wpse64973_load');
function wpse64973_load()
{
    $screen = get_current_screen();

    add_filter("manage_{$screen->id}_columns", 'wpse64973_add_columns');
}

function wpse64973_add_columns($cols)
{
    $cols['title'] = __('Comment Title', 'wpse64973');
    return $cols;
}

add_action('manage_comments_custom_column', 'wpse64973_column_cb', 10, 2);
function wpse64973_column_cb($col, $comment_id)
{
    // you could expand the switch to take care of other custom columns
    switch($col)
    {
        case 'title':
            if($t = get_comment_meta($comment_id, 'pmg_comment_title', true))
            {
                echo esc_html($t);
            }
            else
            {
                esc_html_e('No Title', 'wpse64973');
            }
            break;
    }
}

Good solution!

Worked well for me - put in functions.php without styles

I just hope (but guess not) that it can work with email notifications to be added to the email title. If it doesn't, do anyone have a solution here - which (preferable free) email notification system or plugin would you suggest ?

PS: some added option to "show error or don't save comment if field is empty?" as suggested above would be nice though for some use cases, especially if related to email notifications.