protected function setAsString($field, $value)
    {
        if (in_array($field, $this->getColumns()) && (
                !array_key_exists($field, $this->object) ||
                $this->object[$field] !== $value
            )) {
            $this->dirtyFields[$field] = true;
        }
        $this->object[$field] = (string) $value;

        return $this;
    }