how to create qr code in vb.net Checking for Valid Data in VS .NET

Creation Code 128 in VS .NET Checking for Valid Data

One of the most common tasks you ll want to perform in a data access page is to validate data before the page saves it to the database. In the Housing.mdb sample database, you can find a data access page called dapXmplEmpResRequests. This page is designed to allow employees to enter new reservation requests via a data access page on the company intranet. Of course, the request should contain valid dates and be a request for a reservation in the future, and the check-out date should be later than the check-in date. To see the code that validates any new request, select the sample data access page in the Database window and click the Microsoft Script Editor button on the toolbar. Switch to Script Only View, and you can easily find the following code excerpted from the BeforeUpdate event of the MSODSC object:

Dim ChkInDte, ChkOutDte Dim rs Now check the dates Get the check in and check out dates from the recordset ChkInDte = dscEventInfo.DataPage.Recordset.Fields("CheckInDate") ChkOutDte = dscEventInfo.DataPage.Recordset.Fields("CheckOutDate") If either date is null, warn and cancel If IsNull(ChkInDte) Or IsNull(ChkOutDte) Then MsgBox "Both Check In and Out Dates must be supplied!" dscEventInfo.returnValue = False Exit Sub Make sure the check in date is after the current date. ElseIf datediff("d",ChkInDte,Date())>0 Then MsgBox "Check In Date must be later than today!" dscEventInfo.returnValue = False Exit Sub Finally, make sure the check out date is later than check in. ElseIf datediff("d",ChkOutDte, ChkInDte)>0 Then Msgbox "Check Out Date must be later than Check In Date!" dscEventInfo.returnValue = False Exit Sub End If

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Microsoft Office Access 2003 Inside Out Note Keep in mind that even though you don t have to code the Sub and End Sub statements when you include the object and event information inside the <SCRIPT> tag, your code is still running in the equivalent of a Sub procedure. Therefore, use Exit Sub to exit the procedure. The trick to validating values about to be saved is that your code must fetch the values from the Fields collection of the Recordset object in the current DataPage object. In other ways, the code looks very similar to what you might write in Visual Basic. The code uses the MsgBox function to tell the user about any problems. Rather than set a Cancel variable, the code sets the ReturnValue property of the dscEventInfo object to False to cancel the update when there s a problem.

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None of the tables in the Housing Reservations sample application uses an AutoNumber data type to ensure a unique value in the primary key of a new record. In all the forms that allow adding new rows, you can find Visual Basic code that generates the next number for a new record. So, any data access pages that allow creation of new rows must also generate a unique number, and you can do that with VBScript. For example, you can find the following code in the BeforeUpdate event of the MSODSC object in the example dapXmplDepartments data access page that allows you to edit and insert department information:

<SCRIPT language=vbscript event=BeforeUpdate(dscEventInfo) for=MSODSC> Dim ThisID Dim rs Check to see if we need to supply a Department ID This application does not use AutoNumber ThisID = dscEventInfo.DataPage.Recordset.Fields("DepartmentID") If IsNull(ThisID) Then Fetch the previous high Department ID Set rs = CreateObject("ADODB.Recordset") rs.Open "Select Max(DepartmentID) As MD From tblDepartments", _ MSODSC.Connection If (rs.EOF) Then ThisID = 0 Else ThisID = rs.Fields("MD") End If rs.Close dscEventInfo.DataPage.Recordset.Fields("DepartmentID") = ThisID + 1 End If </SCRIPT>

The original Visual Basic code in the frmDepartments form uses the DMax domain function to look up the highest previous value, but you can t use domain functions in VBScript. If the DepartmentID field has no value, the code opens a recordset on a query to fetch the Max