Comments in WordPress

Comments are a separate entity in the WordPress data structure. They link comments to posts (entries, wp_posts table) and users (wp_users table).

Structure of comments tables in the database

In the WordPress database, comments are managed by two tables: wp_comments and wp_commentmeta. Let's analyze each one.

wp_comments

Contains the main comment data.

// $com - this is the object of the processed comment
wp_update_comment( [
	'comment_ID'   => $com->comment_ID,
	'comment_type' => "archive-$com->comment_type", // archive-question_comment
] );

wp_commentmeta

Contains additional comment data. By default, nothing is written to this table. It is used to extend the commenting functionality and add additional data to comments.

Displaying comments in the theme

To display comments on a page, you need to use the function comments_template() where you want to show the list of comments. This function will make a request and collect the comments for the page.

Also, the theme needs to have a file named comments.php. In this file, you need to describe how to display comments:

• Check if there are comments on the page. This is done using the $comemnts variable, which is set in comments_template() - $comments = & $wp_query->comments and is available in this file. You can also check for the presence of comments on the page using the function have_comments(). Then:
  • if there are comments, use the function wp_list_comments() to display the list of comments.
  • if there are no comments, display a message that there are none.
• Display the commenting form. See comment_form().

Example of the comments.php file from the Twenty Twenty theme:

<?php
/**
 * The template file for displaying the comments and comment form for the
 * Twenty Twenty theme.
 *
 * @package WordPress
 * @subpackage Twenty_Twenty
 * @since Twenty Twenty 1.0
 */

/*
 * If the current post is protected by a password and
 * the visitor has not yet entered the password we will
 * return early without loading the comments.
*/
if ( post_password_required() ) {
	return;
}

if ( $comments ) {
	?>

	<div class="comments" id="comments">

		<?php
		$comments_number = absint( get_comments_number() );
		?>

		<div class="comments-header section-inner small max-percentage">

			<h2 class="comment-reply-title">
				<?php
				if ( ! have_comments() ) {
					_e( 'Leave a comment', 'twentytwenty' );
				}
				elseif ( 1 === $comments_number ) {
					/* translators: %s: Post title. */
					printf( _x( 'One reply on “%s”', 'comments title', 'twentytwenty' ), get_the_title() );
				}
				else {
					printf(
					/* translators: 1: Number of comments, 2: Post title. */
						_nx(
							'%1$s reply on “%2$s”',
							'%1$s replies on “%2$s”',
							$comments_number,
							'comments title',
							'twentytwenty'
						),
						number_format_i18n( $comments_number ),
						get_the_title()
					);
				}

				?>
			</h2><!-- .comments-title -->

		</div><!-- .comments-header -->

		<div class="comments-inner section-inner thin max-percentage">

			<?php
			wp_list_comments(
				array(
					'walker'      => new TwentyTwenty_Walker_Comment(),
					'avatar_size' => 120,
					'style'       => 'div',
				)
			);

			$comment_pagination = paginate_comments_links(
				array(
					'echo'      => false,
					'end_size'  => 0,
					'mid_size'  => 0,
					'next_text' => __( 'Newer Comments', 'twentytwenty' ) . ' <span aria-hidden="true">→</span>',
					'prev_text' => '<span aria-hidden="true">←</span> ' . __( 'Older Comments', 'twentytwenty' ),
				)
			);

			if ( $comment_pagination ) {
				$pagination_classes = '';

				// If we're only showing the "Next" link, add a class indicating so.
				if ( false === strpos( $comment_pagination, 'prev page-numbers' ) ) {
					$pagination_classes = ' only-next';
				}
				?>

				<nav class="comments-pagination pagination<?php echo $pagination_classes; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- static output ?>" aria-label="<?php esc_attr_e( 'Comments', 'twentytwenty' ); ?>">
					<?php echo wp_kses_post( $comment_pagination ); ?>
				</nav>

				<?php
			}
			?>

		</div><!-- .comments-inner -->

	</div><!-- comments -->

	<?php
}

if ( comments_open() || pings_open() ) {

	if ( $comments ) {
		echo '<hr class="styled-separator is-style-wide" aria-hidden="true" />';
	}

	comment_form(
		array(
			'class_form'         => 'section-inner thin max-percentage',
			'title_reply_before' => '<h2 id="reply-title" class="comment-reply-title">',
			'title_reply_after'  => '</h2>',
		)
	);

}
elseif ( is_single() ) {

	if ( $comments ) {
		echo '<hr class="styled-separator is-style-wide" aria-hidden="true" />';
	}

	?>

	<div class="comment-respond" id="respond">

		<p class="comments-closed"><?php _e( 'Comments are closed.', 'twentytwenty' ); ?></p>

	</div><!-- #respond -->

	<?php
}

Setting comment cookies for unauthenticated users

When an unauthenticated user leaves a comment, WP sets cookies to store the entered data. The following cookies are saved:

'comment_author_' . COOKIEHASH
'comment_author_email_' . COOKIEHASH
'comment_author_url_' . COOKIEHASH

// where COOKIEHASH = md5( get_site_option( 'siteurl' ) )

These cookies are saved by the function wp_set_comment_cookies().

By default, this function is hooked to the set_comment_cookies hook in the file /wp-includes/default-filters.php:

add_action( 'set_comment_cookies', 'wp_set_comment_cookies', 10, 3 );

This hook is triggered when a comment is posted through the commenting form comment_form(). That is, when a POST request is sent to the file /wp-comments-post.php:

/**
 * Perform other actions when comment cookies are set.
 *
 * @since 3.4.0
 * @since 4.9.6 The `$cookies_consent` parameter was added.
 *
 * @param WP_Comment $comment         Comment object.
 * @param WP_User    $user            Comment author's user object. The user may not exist.
 * @param bool       $cookies_consent Comment author's consent to store cookies.
 */
do_action( 'set_comment_cookies', $comment, $user, $cookies_consent );

Use wp_get_current_commenter() to obtain the data of these cookies.

Comment functions

This is a list of frequently used functions. See the full list here.