CODE EXAMPLE FOR PHP

how to add custom field in comment form in wordpress

add_filter('comment_form_default_fields','custom_fields');
function custom_fields($fields) {
		$commenter = wp_get_current_commenter();
		$req = get_option( 'require_name_email' );
		$aria_req = ( $req ? " aria-required='true'" : '' );
		$fields[ 'email' ] = '<p class="comment-form-email">'.
			'<label for="email">' . __( 'Email' ) . '</label>'.
			( $req ? '<span class="required">*</span>' : '' ).
			'<input id="email" name="email" type="text" value="'. esc_attr( $commenter['comment_author_email'] ) . 
			'" size="30"  tabindex="2"' . $aria_req . ' /></p>';
}
// Add fields after default fields above the comment box, always visible
add_action( 'comment_form_logged_in_after', 'additional_fields' );
add_action( 'comment_form_after_fields', 'additional_fields' );
function additional_fields () {
	echo '<p class="comment-form-rating">'.
	'<label for="rating">'. __('Rating') . '<span class="required">*</span></label>
	<span class="commentratingbox">';
	
	for( $i=1; $i <= 5; $i++ )
	echo '<span class="commentrating"><input type="radio" name="rating" id="rating" value="'. $i .'"/>'. $i .'</span>';
	echo'</span></p>';
}
// Save the comment meta data along with comment
add_action( 'comment_post', 'save_comment_meta_data' );
function save_comment_meta_data( $comment_id ) {
	if ( ( isset( $_POST['rating'] ) ) && ( $_POST['rating'] != '') )
	$rating = wp_filter_nohtml_kses($_POST['rating']);
	add_comment_meta( $comment_id, 'rating', $rating );
}
// Add the filter to check if the comment meta data has been filled or not
add_filter( 'preprocess_comment', 'verify_comment_meta_data' );
function verify_comment_meta_data( $commentdata ) {
	if ( ! isset( $_POST['rating'] ) )
	wp_die( __( 'Error: You did not add your rating. Hit the BACK button of your Web browser and resubmit your comment with rating.' ) );
	return $commentdata;
}
//Add an edit option in comment edit screen  
add_action( 'add_meta_boxes_comment', 'extend_comment_add_meta_box' );
function extend_comment_add_meta_box() {
    add_meta_box( 'title', __( 'Comment Metadata - Extend Comment' ), 'extend_comment_meta_box', 'comment', 'normal', 'high' );
}
function extend_comment_meta_box ( $comment ) {
    $rating = get_comment_meta( $comment->comment_ID, 'rating', true );
    wp_nonce_field( 'extend_comment_update', 'extend_comment_update', false );
    ?>
    <p>
        <label for="rating"><?php _e( 'Rating: ' ); ?></label>
			<span class="commentratingbox">
			<?php for( $i=1; $i <= 5; $i++ ) {
				echo '<span class="commentrating"><input type="radio" name="rating" id="rating" value="'. $i .'"';
				if ( $rating == $i ) echo ' checked="checked"';
				echo ' />'. $i .' </span>'; 
				}
			?>
			</span>
    </p>
    <?php
}
// Update comment meta data from comment edit screen 
add_action( 'edit_comment', 'extend_comment_edit_metafields' );
function extend_comment_edit_metafields( $comment_id ) {
    if( ! isset( $_POST['extend_comment_update'] ) || ! wp_verify_nonce( $_POST['extend_comment_update'], 'extend_comment_update' ) ) return;

	if ( ( isset( $_POST['rating'] ) ) && ( $_POST['rating'] != '') ):
	$rating = wp_filter_nohtml_kses($_POST['rating']);
	update_comment_meta( $comment_id, 'rating', $rating );
	else :
	delete_comment_meta( $comment_id, 'rating');
	endif;
}
// Add the comment meta (saved earlier) to the comment text 
// You can also output the comment meta values directly in comments template  
add_filter( 'comment_text', 'modify_comment');
function modify_comment( $text ){
	$plugin_url_path = WP_PLUGIN_URL;

	if( $commenttitle = get_comment_meta( get_comment_ID(), 'title', true ) ) {
		$commenttitle = '<strong>' . esc_attr( $commenttitle ) . '</strong><br/>';
		$text = $commenttitle . $text;
	} 

	if( $commentrating = get_comment_meta( get_comment_ID(), 'rating', true ) ) {
		$commentrating = '<p class="comment-rating">	<img src="'. $plugin_url_path .
		'/ExtendComment/images/'. $commentrating . 'star.gif"/><br/>Rating: <strong>'. $commentrating .' / 5</strong></p>';
		$text = $text . $commentrating;
		return $text;		
	} else {
		return $text;		
	}	 
}
function average_rating() {
global $wpdb;
$post_id = get_the_ID();
$ratings = $wpdb->get_results("

    SELECT $wpdb->commentmeta.meta_value
    FROM $wpdb->commentmeta
    INNER JOIN $wpdb->comments on $wpdb->comments.comment_id=$wpdb->commentmeta.comment_id
    WHERE $wpdb->commentmeta.meta_key='rating' 
    AND $wpdb->comments.comment_post_id=$post_id 
    AND $wpdb->comments.comment_approved =1

    ");
$counter = 0;
$average_rating = 0;    
if ($ratings) {
    foreach ($ratings as $rating) {
        $average_rating = $average_rating + $rating->meta_value;
        $counter++;
    } 
    //round the average to the nearast 1/2 point
    return (round(($average_rating/$counter)*2,0)/2);  
} else {
    //no ratings
    return 'no rating';
}}