Question

Basically what I need to do is to insert into table Reservation a vehicleID, startDate and endDate.

I can do that fine but I’d like to validate it so that it cannot be inserted for that vehicleID if the current date is <= endDate as currently I can just keep adding to the Reservation table on the same vehicleID

This is just the simple insert SQL statement.

strInsert = String.Format("Insert into Reservation (VehicleID, startDate, enddate) VALUES ('{0}','{1}','{2}')", vID, now, now5)

Regards.

Answer 1

How about not attempting an insert if today’s date is less than the enddate you are inserting?

If Date.Today <= now5 Then
   Throw New Exception("Invalid Date")
Else
  strInsert = String.Format("Insert into Reservation (VehicleID, startDate, enddate) VALUES ('{0}','{1}','{2}')", vID, now, now5)
End If

UPDATE

If you are implementing this all in SQL, then I recommend using a stored procedure, but in either case the logic is the same. Check to see if any reservations exist that overlap today and if they do, throw an exception from SQL.

Note that GETDATE() is not quite the right value to use since it returns the current timestamp, but without know how the values are stored, it is used as an approximation and can be cleaned up later.

CREATE PROCEDURE s_AddReservation
    @VehicleID   INT ,
    @StartDate   DATETIME ,
    @EndDate     DATETIME
AS
    IF EXISTS(SELECT 1
                FROM Reservation
               WHERE VehicleID = @VehicleID
                 AND StartDate <= GETDATE()
                 AND EndDate >= GETDATE())
      BEGIN
        RAISERROR('This care has already been rented', 16, 1);
      END
    ELSE
      BEGIN
        Insert into Reservation (VehicleID, startDate, enddate) VALUES (@VehicleID, @StartDate, @EndDate)
      END
GO

To call this stored procedure from your code:

var oCommand = new SqlCommand('s_AddReservation', conn);
oCommand.CommandType = CommandType.StoredProcedure;
oCommand.Parameters.AddWithValue("@VehicleID", vID);
oCommand.Parameters.AddWithValue("@StartDate", now);
oCommand.Parameters.AddWithValue("@EndDate", now5);

oCommand.ExecuteNonQuery();