protected function addUpdateExchangeRate($currencyFrom, $currencyTo, $rate)
    {
        if (!in_array($currencyTo, $this->managedCurrencies)) {
            return false;
        }
        
        $exchangeRate = $this->currencyRateRepository->findOneBy([
            'currencyFrom' => $currencyFrom,
            'currencyTo'   => $currencyTo,
        ]);
        
        if (null === $exchangeRate) {
            $exchangeRate = new CurrencyRate();
            $exchangeRate->setCurrencyFrom($currencyFrom);
            $exchangeRate->setCurrencyTo($currencyTo);
            $exchangeRate->setExchangeRate($rate);
            $this->helper->getEntityManager()->persist($exchangeRate);
        } else {
            $exchangeRate->setExchangeRate($rate);
        }
        
        return true;
    }