How to check if resource is msCategory by id?

Question

MODX

Actually the question is:
how to check if the resource is msCategory by id?
If not, then get the id of all child resources with the msCategory class.

Answer 1

If you need child categories of the 1st nesting level

if (!$cat = $modx->getObject('msCategory', $id)) {
    $res = $modx->getCollection('msCategory', array('parent' => $id));
    $ids = array_keys($res); // Массив с id дочерних категорий
}