public function columnOrder($columnName, $orderDirection)
    {
        if (!is_string($orderDirection)) {
            throw new \InvalidArgumentException('$orderDirection "' . $orderDirection . '" needs to be a string');
        }
        $isAscOrdering = $orderDirection === "asc" ? true : false;
        $this->columnOrders[] = new ColumnOrder($columnName, $isAscOrdering);
        return $this;
    }