Answered Cannot retrieve ID from the object after save

<object class="ltMarker" table="marker" extends="ltObject">
    <field key="id" dbtype="bigint" precision="20" phptype="integer" attributes="unsigned" null="false" generated="native" />
    <field key="type" dbtype="int" precision="11" phptype="integer" null="false" />
    <field key="lat" dbtype="decimal" precision="17,14" phptype="float" null="false" />
    <field key="lng" dbtype="decimal" precision="17,14" phptype="float" null="false" />
    <field key="created_on" dbtype="datetime" phptype="datetime" null="true" />
    <field key="created_user_id" dbtype="int" precision="10" attributes="unsigned" phptype="integer" null="true" />
    <field key="created_user_ip" dbtype="varchar" precision="45" phptype="string" null="true" />
    <field key="updated_on" dbtype="datetime" phptype="datetime" null="true" />
    <field key="updated_user_id" dbtype="int" precision="10" attributes="unsigned" phptype="integer" null="true" />
    <field key="updated_user_ip" dbtype="varchar" precision="45" phptype="string" null="true" />

    <index alias="PRIMARY" name="PRIMARY" primary="true" unique="true" type="BTREE" >
        <column key="id" length="" collation="A" null="false" />
    </index>
</object>

$schoolMarker = null;
if (!empty($_POST['schoolMarker'])) {
  $schoolMarker = $modx->newObject('ltMarker');
  $schoolMarker->set('type', $schoolMarker::TYPE_SCHOOL_MARKER);
  $schoolMarker->set('lat', $_POST['schoolMarker']['lat']);
  $schoolMarker->set('lng', $_POST['schoolMarker']['lng']);
  $schoolMarker->set('created_on', strftime("%Y-%m-%d %H:%M:%S"));
  $schoolMarker->set('created_user_id', $modx->user->get('id'));
  $schoolMarker->set('created_user_ip', $schoolMarker->getIp());
  $schoolMarker->set('updated_on', strftime("%Y-%m-%d %H:%M:%S"));
  $schoolMarker->set('updated_user_id', $modx->user->get('id'));
  $schoolMarker->set('updated_user_ip', $schoolMarker->getIp());
  $schoolMarker->save();
  $output .= '<pre>ID:'.$schoolMarker->get('id').'</pre>';
}
$id = $schoolMarker->get('id');
$output .= '<pre>ID:'.$id.'</pre>';
$output .= '<pre>ID:'.$schoolMarker->getPrimaryKey().'</pre>';
$output .= '<pre>ID:'.$modx->lastInsertId().'</pre>';
return $output;