// related posts
// see https://github.com/scribu/wp-posts-to-posts/wiki/Basic-usage
function my_connection_types() {
p2p_register_connection_type( array(
'name' => 'posts_to_pages',
'from' => 'clients',
'to' => 'portfolio'
) );
}
add_action( 'p2p_init', 'my_connection_types' );