How to Orderby Comments by post title?

Question

Whatever I tried so far didn't work. So I started looking everywhere for a few days now, trying to figure out how to order comments by the title of the post they are made into. (I tried a meta_value also, but it seems I didn't do it right). I read the wp codex. Here is what I am trying to make sort comments by post title, but there is no title or post_title parameter for the orderby of comments. Any help will be appreciated.

<?php $args = array(
    'status' => 'approve',
    'post_status' => 'publish',
    'post_type' => 'post',
    'orderby' => 'title',
    'order' => 'DESC'
);

$comments_query = new WP_Comment_Query; ?>

Answer 1

The WP_Comment_Query class supports ordering by:

'comment_agent',
'comment_approved', 
'comment_author',
'comment_author_email', 
'comment_author_IP',
'comment_author_url', 
'comment_content', 
'comment_date',
'comment_date_gmt', 
'comment_ID', 
'comment_karma',
'comment_parent', 
'comment_post_ID', 
'comment_type',
'user_id', 
'comment__in', 
'meta_value', 
'meta_value_num',

There's a way to adjust it via filters so we can support ordering by the post title:

$args = [
    'status'       => 'approve',
    'post_status'  => 'publish',
    'post_type'    => 'post',
    'orderby'      => '_post_title', // <-- Our custom orderby value
    'order'        => 'DESC'
];

$comment_query = new WP_Comment_Query( $args ); 

A simple demo plugin to support the _post_title ordering could be in PHP 7:

/**
 * Adjust orderby comments clause
 */

add_filter( 'comments_clauses', function( $clauses, \WP_Comment_Query $cq ) use ( &$wpdb )
{   
    $qv      = $cq->query_vars;
    $orderby = $qv['orderby'] ?? '';
    $order   = $qv['order'] ?? 'ASC';

    if( 
           '_post_title' === $orderby 
        && in_array( strtoupper( $order ), [ 'ASC', 'DESC' ], true ) 
    )
        $clauses[ 'orderby' ] = " {$wpdb->posts}.post_title {$order},
            {$wpdb->comments}.comment_ID {$order} "; 


    return $clauses;
}, 10, 2 );

and then to make sure the posts table is joined to the comment table, we can set the post type parameter to 'post' if it's missing:

/**
 * Make usre we have the posts table joined by making sure the post_type isn't empty.
 */

add_action( 'pre_get_comments', function( \WP_Comment_Query $cq )
{
    $qv      = &$cq->query_vars;
    $orderby = $qv['orderby'] ?? '';

    if( '_post_title' === $orderby && empty( $qv['post_type'] ) )
        $qv['post_type'] = 'post';

} );

Note that this kind of query:

SELECT  wp_comments.comment_ID 
    FROM wp_comments JOIN wp_posts ON wp_posts.ID = wp_comments.comment_post_ID     
    WHERE ( comment_approved = '1' ) 
        AND  wp_posts.post_status IN ('publish') 
        AND  wp_posts.post_type IN ('post')  
    ORDER BY  wp_posts.post_title DESC, wp_comments.comment_ID DESC  

is not efficient as it uses temporary and filesort.

Hope you can adjust it further to your needs.