public function getDataEntry($id, $key)
    {
        if (!isset($this->data[$id])) {
            throw new InvalidArgumentException("Missing row with id $id.");
        }
        if ($this->isAlias($key)) {
            $key = $this->trimAlias($key);
        }
        if (!array_key_exists($key, $this->data[$id])) {
            throw new InvalidArgumentException("Missing '$key' column in row with id $id.", self::ERROR_MISSING_COLUMN);
        }
        return $this->data[$id][$key];
    }