$this->Thread->recursive = -1;
$threads = $this->paginate('Thread');
$this->set('threads', $threads);
    
$thread_ids = array();
for($i=0; $i<count($threads); $i++) {
    $thread_ids[] = $threads[$i]['Thread']['id'];
}
    
$this->Message->recursive = -1;
$messages = $this->Message->find('all', array(
    'conditions' => array(
        'Message.created <=' => date("Y-m-d H:i:s"),
        'thread_id' => $thread_ids
    ),
    'group' => 'Message.thread_id',
    'fields' => array('thread_id', 'COUNT(*) as `count`')
));
$count = array();
for($i=0; $i<count($messages); $i++) {
    $count[$messages[$i]['Message']['thread_id']] = $messages[$i]['0']['count'];
}
    
for($i=0; $i<count($threads); $i++)  {
    $id = $threads[$i]['Thread']['id'];
    $threads[$i]['Thread']['messages_count'] = $count[$id];
}
    
debug($threads);

This approach requires only two queries in any case.

echo count($post['ApprovedComment'])

?

@Simon: Yes, your code snippet is more efficient than what I wrote.

@Ivo, Michal, GreyCells: To make it work with GROUP BY I have to use a manual query as CakePHP no longer uses a join:

$this->execute('SELECT Post.*, COUNT(Comment.id) AS comment_count FROM posts AS Post LEFT OUTER JOIN comments AS Comment ON Comment.post_id = Post.id GROUP BY Post.id');

$conditions = array(‘Post.id’ => 42, ‘1=1 GROUP BY Post.id);

I think the same applies to HAVING (i.e. ‘1=1 HAVING count(Comment.id) > 5)

I agree with Ivo – approach with GROUP BY is much faster.
I usually write more complex queries by myself – I don`t try to fit the query to CakePHP manner.

BTW: if you use PostgreSQL, you can write:
‘COUNT(Comment.id) as Post__comment_count’

And CakePHP will parse the column to own array format automaticaly.

Regards