Manually Curated Related Posts - Establish the Connection

postconnections.php

<?php

/**
 * Related Post Connection
 * Forked from: 
 * @author Bill Erickson
 * @link http://www.billerickson.net/manually-curated-related-posts/
 *
 * @uses Posts2Posts
 * @link https://github.com/scribu/wp-posts-to-posts/wiki
 */
function be_post_type_connections() {

	p2p_register_connection_type( array(
		'name' => 'courses_to_units', // unique name
		'from' => 'course',
		'to' => 'unit',
	) );

	p2p_register_connection_type( array(
		'name' => 'units_to_lessons', // unique name
		'from' => 'unit',
		'to' => 'lesson',
	) );	
		
	p2p_register_connection_type( array(
		'name' => 'lessons_to_sublessons', // unique name
		'from' => 'lesson',
		'to' => 'sublesson',
	) );	
}
add_action( 'p2p_init', 'be_post_type_connections' );