Get nav menu ID by "page id" and build sub navigation menu for that parent - WordPress PHP code

subNavMenuByPageID.php

<?php
//this code is located in themes/{theme name}/page-templates/mypagetemplate.php in an area where i want to output the menu

//Get the Post/Page Id of the parent
if ($post->post_parent)
{
    //go through post ancestors to find parent
    $ancestors = get_post_ancestors($post->ID);
    $parentPostId = $ancestors[count($ancestors) - 1];
}
else
{
    //this page is the parent us the Post Id of this page
    $parentPostId = $post->ID;
}
$parentNavMenuId=0;
//Set this to your menu
$menu_name = 'primary';

if (( $locations = get_nav_menu_locations() ) && isset($locations[$menu_name]))
{
    $menu = wp_get_nav_menu_object($locations[$menu_name]);
    $menu_items = wp_get_nav_menu_items($menu->term_id);
    $menu_list = '<ul id="menu-' . $menu_name . '">';
    
    //Find parent menu id by the post id
    foreach ((array) $menu_items as $key => $menu_item)
    {
        if ($menu_item->object_id == $parentPostId)
        {
            $parentNavMenuIds[] = $menu_item->ID;
        }
    }
    foreach ((array) $menu_items as $key => $menu_item)
    {
        if (in_array($menu_item->menu_item_parent,$parentNavMenuIds))
        {
            $title = $menu_item->title;
            $url = $menu_item->url;
            $menu_list .= '<li><a href="' . $url . '">' . $title . '</a></li>';
        }
    }
    $menu_list .= '</ul>';
}
else
{
    $menu_list = '<ul><li>Menu "' . $menu_name . '" not defined.</li></ul>';
}
echo $menu_list;
?>