How to check does getObjectGraph work?

$retArray = array();
$polylineMarkerObj = $modx->newObject('ltPolylineMarker');
$graph = '{
	"PrincipalRoute":{
		"Polyline":{
			"PolylineMarker":{
			}
		}
	},
	"SchoolMarker":{
	}
}';
$criteria = $modx->newQuery('ltPrincipalMap');
$criteria->where(array(
	'ltPrincipalMap.user_id' => $modx->user->get('id'),
	'PolylineMarker.type' => $polylineMarkerObj::TYPE_PATH_MARKER
));
$criteria->sortby('PrincipalRoute.index','ASC');
$criteria->bindGraph($graph);
//$criteria->prepare();
//$modx->log(modX::LOG_LEVEL_ERROR, $criteria->toSQL());
$principalMap = $modx->getObjectGraph('ltPrincipalMap', $graph, $criteria);
if (is_object($principalMap)) {
	$schoolMarker = $principalMap->getOne('SchoolMarker');
	$retArray['schoolMarker']['lat'] = $schoolMarker->get('lat');
	$retArray['schoolMarker']['lng'] = $schoolMarker->get('lng');
	$retArray['polylines'] = array();
	$principalRoutes = $principalMap->getMany('PrincipalRoute');
	$index = 0;
	foreach ($principalRoutes as $principalRoute) {
		$retArray['polylines'][$index] = array();
		$polyline = $principalRoute->getOne('Polyline');
		$polylineMarkers = $polyline->getMany('PolylineMarker', array('type' => $polylineMarkerObj::TYPE_PATH_MARKER));
		$idx = 0;
		foreach ($polylineMarkers as $polylineMarker) {
			$retArray['polylines'][$index]['path'][$idx] = array('lat' => $polylineMarker->get('lat'), 'lng' => $polylineMarker->get('lng'));
			$idx++;
		}
		$index++;
	}
	return '{success:true, data:'.json_encode($retArray).'}';
} else {
	return '{success:false, msg:"could retrieve principal map"}';
}

$retArray['schoolMarker']['lat'] = $principalMap->SchoolMarker->get('lat');

$retArray = array();
$polylineMarkerObj = $modx->newObject('ltPolylineMarker');
$graph = '{
	"PrincipalRoute":{
		"Polyline":{
			"PolylineMarker":{
			}
		}
	},
	"SchoolMarker":{
	}
}';
$criteria = $modx->newQuery('ltPrincipalMap');
$criteria->where(array(
	'ltPrincipalMap.user_id' => $modx->user->get('id'),
	'PolylineMarker.type' => $polylineMarkerObj::TYPE_PATH_MARKER
));
$criteria->sortby('PrincipalRoute.index','ASC');
$criteria->bindGraph($graph);
//$criteria->prepare();
//$modx->log(modX::LOG_LEVEL_ERROR, $criteria->toSQL());
$principalMap = $modx->getObjectGraph('ltPrincipalMap', $graph, $criteria);
if (is_object($principalMap)) {
	$schoolMarker = $principalMap->SchoolMarker;
	$retArray['schoolMarker']['lat'] = $schoolMarker->get('lat');
	$retArray['schoolMarker']['lng'] = $schoolMarker->get('lng');
	$retArray['polylines'] = array();
	$principalRoutes = $principalMap->PrincipalRoute;
	$index = 0;
	foreach ($principalRoutes as $principalRoute) {
		$retArray['polylines'][$index] = array();
		$polyline = $principalRoute->Polyline;
		$polylineMarkers = $polyline->getMany('PolylineMarker', array('type' => $polylineMarkerObj::TYPE_PATH_MARKER));
		$idx = 0;
		foreach ($polylineMarkers as $polylineMarker) {
			$retArray['polylines'][$index]['path'][$idx] = array('lat' => $polylineMarker->get('lat'), 'lng' => $polylineMarker->get('lng'));
			$idx++;
		}
		$index++;
	}
	return '{success:true, data:'.json_encode($retArray).'}';
} else {
	return '{success:false, msg:"could retrieve principal map"}';
}

SELECT 
  `ltPrincipalMap`.`id` AS `ltPrincipalMap_id`, 
  `ltPrincipalMap`.`user_id` AS `ltPrincipalMap_user_id`, 
  `ltPrincipalMap`.`school_marker_id` AS `ltPrincipalMap_school_marker_id`, 
  `ltPrincipalMap`.`submitted` AS `ltPrincipalMap_submitted`, 
  `ltPrincipalMap`.`created_on` AS `ltPrincipalMap_created_on`, 
  `ltPrincipalMap`.`created_user_id` AS `ltPrincipalMap_created_user_id`, 
  `ltPrincipalMap`.`created_user_ip` AS `ltPrincipalMap_created_user_ip`, 
  `ltPrincipalMap`.`updated_on` AS `ltPrincipalMap_updated_on`, 
  `ltPrincipalMap`.`updated_user_id` AS `ltPrincipalMap_updated_user_id`, 
  `ltPrincipalMap`.`updated_user_ip` AS `ltPrincipalMap_updated_user_ip`, 
  `PrincipalRoute`.`id` AS `PrincipalRoute_id`, 
  `PrincipalRoute`.`polyline_id` AS `PrincipalRoute_polyline_id`, 
  `PrincipalRoute`.`principal_map_id` AS `PrincipalRoute_principal_map_id`, 
  `PrincipalRoute`.`index` AS `PrincipalRoute_index`, 
  `PrincipalRoute`.`created_on` AS `PrincipalRoute_created_on`, 
  `PrincipalRoute`.`created_user_id` AS `PrincipalRoute_created_user_id`, 
  `PrincipalRoute`.`created_user_ip` AS `PrincipalRoute_created_user_ip`, 
  `PrincipalRoute`.`updated_on` AS `PrincipalRoute_updated_on`, 
  `PrincipalRoute`.`updated_user_id` AS `PrincipalRoute_updated_user_id`, 
  `PrincipalRoute`.`updated_user_ip` AS `PrincipalRoute_updated_user_ip`, 
  `Polyline`.`id` AS `Polyline_id`, 
  `Polyline`.`created_on` AS `Polyline_created_on`, 
  `Polyline`.`created_user_id` AS `Polyline_created_user_id`, 
  `Polyline`.`created_user_ip` AS `Polyline_created_user_ip`, 
  `Polyline`.`updated_on` AS `Polyline_updated_on`, 
  `Polyline`.`updated_user_id` AS `Polyline_updated_user_id`, 
  `Polyline`.`updated_user_ip` AS `Polyline_updated_user_ip`, 
  `PolylineMarker`.`id` AS `PolylineMarker_id`, 
  `PolylineMarker`.`polyline_id` AS `PolylineMarker_polyline_id`, 
  `PolylineMarker`.`type` AS `PolylineMarker_type`, 
  `PolylineMarker`.`lat` AS `PolylineMarker_lat`, 
  `PolylineMarker`.`lng` AS `PolylineMarker_lng`, 
  `PolylineMarker`.`created_on` AS `PolylineMarker_created_on`, 
  `PolylineMarker`.`created_user_id` AS `PolylineMarker_created_user_id`, 
  `PolylineMarker`.`created_user_ip` AS `PolylineMarker_created_user_ip`, 
  `PolylineMarker`.`updated_on` AS `PolylineMarker_updated_on`, 
  `PolylineMarker`.`updated_user_id` AS `PolylineMarker_updated_user_id`, 
  `PolylineMarker`.`updated_user_ip` AS `PolylineMarker_updated_user_ip`, 
  `SchoolMarker`.`id` AS `SchoolMarker_id`, 
  `SchoolMarker`.`type` AS `SchoolMarker_type`, 
  `SchoolMarker`.`lat` AS `SchoolMarker_lat`, 
  `SchoolMarker`.`lng` AS `SchoolMarker_lng`, 
  `SchoolMarker`.`created_on` AS `SchoolMarker_created_on`, 
  `SchoolMarker`.`created_user_id` AS `SchoolMarker_created_user_id`, 
  `SchoolMarker`.`created_user_ip` AS `SchoolMarker_created_user_ip`, 
  `SchoolMarker`.`updated_on` AS `SchoolMarker_updated_on`, 
  `SchoolMarker`.`updated_user_id` AS `SchoolMarker_updated_user_id`, 
  `SchoolMarker`.`updated_user_ip` AS `SchoolMarker_updated_user_ip`
FROM 
  `custom_principal_map` AS `ltPrincipalMap` 
LEFT JOIN 
  `custom_principal_route` `PrincipalRoute` ON `ltPrincipalMap`.`id` = `PrincipalRoute`.`principal_map_id` 
LEFT JOIN 
  `custom_polyline` `Polyline` ON `PrincipalRoute`.`polyline_id` = `Polyline`.`id` 
LEFT JOIN 
  `custom_polyline_marker` `PolylineMarker` ON `Polyline`.`id` = `PolylineMarker`.`polyline_id` 
LEFT JOIN 
  `custom_marker` `SchoolMarker` ON `ltPrincipalMap`.`school_marker_id` = `SchoolMarker`.`id` 
WHERE  
  ( `ltPrincipalMap`.`user_id` = 2 AND `PolylineMarker`.`type` = '3' )  
ORDER BY 
  PrincipalRoute.index ASC, `ltPrincipalMap`.`id` ASC 

$polylineMarkers = $polyline->PolylineMarker;

$polylineMarkers = $polyline->getMany('PolylineMarker', array('type' => $polylineMarkerObj::TYPE_PATH_MARKER));