vue-wp/plugins/cia-endpoints/includes/related-items.php

<?php

include(formats.php);

function grab_ids_related_to_and_from($id_to_remove, $p2p_res) {
    $related_to_ids = array_map(function($post) {
        return (int)$post->p2p_to;
    }, $p2p_res);
    $related_from_ids = array_map(function($post) {
        return (int)$post->p2p_from;
    }, $p2p_res);

    $unfiltered = array_merge($related_to_ids, $related_from_ids);
    $deduped = array_unique($unfiltered);

    return array_diff( $deduped, array($id_to_remove) );
}

function prepare_related_items($args) {
    // Rearrange what fields get shown
    $collection = array();
    forEach( get_posts($args) as $item ) {
        $collection[$item->ID] = default_post_format($item, true);
    }
    return $collection;
}

function p2p_related_to($id, $type) {
    global $wpdb;
    $to_type = '%_to_' . $type;
    $from_type = $type . '_to_%';

    $res = $wpdb->get_results($wpdb->prepare(
        "SELECT * FROM wp_p2p
        WHERE p2p_from = %d
        OR p2p_to = %d",
        $id, $id
    ));

    $related_posts_ids = grab_ids_related_to_and_from($id, $res);

    // Use IDs to get posts from the wpdb
    $args = array(
        'numberposts' => -1,
        'post_type' => 'any',
        'include' => $related_posts_ids
    );
    wp_reset_postdata();

    return prepare_related_items($args);
}

?>