public static string OverlappingReservationsExist(Reservation reservation, IReservationRepo _repository) { if (reservation.Status == "Cancelled") { return(string.Empty); } var reservations = _repository.GetActiveReservations(1); var overlappingReservation = reservations.FirstOrDefault( b => reservation.ArrivalDate < b.DepartureDate && b.ArrivalDate < reservation.DepartureDate); return(overlappingReservation == null ? string.Empty : overlappingReservation.Reference); }