I have a custom post type that has a one to many relationship with another custom post type. Call them lesson and topics. Currently, I get $topics as

$args = array(
                'meta_key' => 'lesson_id',
                'meta_value' => $post['post']->ID,
                'post_type' => 'plugin-topic',
                'post_status' => 'published',
                'posts_per_page' => -1
            );
            $les_topics = get_posts($args);

However, when the $lesson object is created by wordpress for first time, I would like to add $topics to it so that I can reference as $lesson->topics.

Can someone tell me the appropriate filter or action to use to accomplish that? I saw this

Adding additional data to WP_Post object

which suggests I shouldn’t even do what I am asking to do but it isn’t clear why this would be a bad thing.

thanks!
Brian