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

<?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($post_ids) {
    // Rearrange what fields get shown
    $collection = array();

    // Use IDs to get posts from the wpdb
    $args = [
        'numberposts' => -1,
        'post_type' => 'any',
        'include' => $post_ids
    ];
    
    $related_items = get_posts($args);
    forEach( $related_items as $item ) {
        $collection[$item->ID] = default_post_format($item, false);
    }
    return $collection;
}

function p2p_related_to($id, $type) {
    global $wpdb;
    $sql = $wpdb->prepare(
        "SELECT * FROM wp_p2p
        WHERE p2p_from = %d
        OR p2p_to = %d",
        $id, $id
    );
    $res = $wpdb->get_results($sql);
    
    $related_posts_ids = grab_ids_related_to_and_from($id, $res);
    $related_posts = prepare_related_items($related_posts_ids);
    
    if(empty($related_posts_ids)) {
        return [];
    } else {
        return $related_posts;
    }
}

?>