Folder::getSize

public function getSize($filter = null)
{
	$query = new Query(FileTable::getEntity());
	$query
		->registerRuntimeField('', new ExpressionField('FILE_SIZE', 'SUM(SIZE)'))
		->addSelect('FILE_SIZE')
		->addFilter('=PATH_CHILD.PARENT_ID', $this->getRealObjectId())
		->addFilter('=STORAGE_ID', $this->getStorageId())
		->addFilter('=TYPE', FileTable::TYPE)
		->addFilter('=DELETED_TYPE', FileTable::DELETED_TYPE_NONE)
	;

	$result = $query->exec();
	$row = $result->fetch();
	if (isset($row['FILE_SIZE']))
	{
		return $row['FILE_SIZE'];
	}

	return null;
}