comment.php

<?php

class Model_Builder_Comment extends Jelly_Builder {
    public function get_user_posts_comments(Model_Author $author)
    {
        // Get author's posts ids
        $post_ids = $author->get('posts')->as_array('id');
        // Get the comments that belong to these posts
        return $this->where('post_id', 'IN', $post_ids);
    }
}