private string GetCacheKey(GetExchangeRates request) => $"{nameof(GetExchangeRates)}-{request.Date}";
public Task <IEnumerable <ExchangeRate> > Handle(GetExchangeRates request, CancellationToken cancellationToken) { return(Task.FromResult(_appCache.GetOrAdd(GetCacheKey(request), () => Query(request.Date), DateTimeOffset.Now.AddHours(8)))); }