private async void CreateOnClick(object sender, RoutedEventArgs e)
        {
            Errors = new List <string>();
            var cust = new Customer()
            {
                FirstName = Input.FirstName,
                LastName  = Input.LastName,
                Email     = Input.Email,
                Phone     = Input.Phone
            };
            var room = await businessLogic.GetRoomByNumber(Input.RoomNumber);

            if (room == null)
            {
                Errors.Add("Podano zły numer pokoju.");
                ErrorTable.ItemsSource = Errors;
                return;
            }

            var res = new Reservation()
            {
                FromDate       = DateTime.Parse(Input.FromDate),
                ToDate         = DateTime.Parse(Input.ToDate),
                NumberOfGuests = Input.NumberOfGuests,
                Customer       = cust,
                Room           = room
            };
            var result = isNewRecord ? await businessLogic.AddReservation(res) : await businessLogic.UpdateReservation(res);

            if (result.Succeeded)
            {
                this.Close();
                return;
            }
            foreach (var err in result.ErrorMessages)
            {
                Errors.Add(err);
            }
            ErrorTable.ItemsSource = Errors;
            return;
        }