public static void RemoveRent(RentClass rent)
 {
     rent.CurrentCar.CarStatus     = false;
     rent.CurrentCar.CurrentClient = null;
     SQLCars.GetInstance().Update(rent.CurrentCar);
     SQLRents.GetInstance().Remove(rent.RentId.ToString());
     Rent.Remove(rent);
 }
 public static void AddNewRent(RentClass rentToAdd)
 {
     if (rentToAdd != null)
     {
         rentToAdd.CurrentCar.CarStatus     = true;
         rentToAdd.CurrentCar.CurrentClient = rentToAdd.CurrentClient;
         SQLCars.GetInstance().Update(rentToAdd.CurrentCar);
         SQLRents.GetInstance().Create(rentToAdd);
         Rent.Add(rentToAdd);
         TransactionService.NewTransaction(rentToAdd.CurrentCar.Cost, rentToAdd.CurrentClient);
     }
     else
     {
         throw new ArgumentNullException("rentToAdd can't be null!");
     }
 }