I am trying to learn how to use ADO.Net from a book. As I am just new to programming this is turning out to be quite an event!
I have managed to populate an msAccess database with the relevant user input information however what I need to do now is search the database's "Date" column to see if there is already a date matching the users "chosen date" in the database...Gee that's long winded!
When the user inputs a chosen date for an event, which is not already chosen and stored in the db, the db accepts all other input data. However if the chosen event date is already in the db this message occurs:

An unhandled exception of type 'System.Data.ConstraintException' occurred in system.data.dll

Additional information: Column 'Date' is constrained to be unique. Value '23/04/2002 00:00:00' is already present.


Is there any way of turning this into a messagebox.show to inform the user that the date is already taken?
I really hope someone out there can help me...I'm starting to get desperate!
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Hi sconineuk
I am also new to VB.Net. Hope following Code will solve your problem.

Dim queryString As String = "Select * from [table] where Date="& datatimePicker.value & "
Dim command As New OledbCommand(queryString, connection)
Dim reader As SqlDataReader = command.ExecuteReader()

' Check Date
if reader.Read()
    messagebox.show "Date Already there. Select Other Date"
End While
        ' Call Close when done reading.
reader.Close()

Here connection is your Existing connection Name.

hi
you can use try catch block
or if you want to use MessageBox
you can easily use messagebox.show() in vb.net

Charul Shukla

Thank you two for your reply but I still cant get it to work!
I feel so unintelligent!
Can you explain to me as simply as you can how a Try/Catch works
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This is the error message that comes from running this and choosing an already saved date:

An unhandled exception of type 'System.NullReferenceException' occurred in WindowsApplication1.exe

Additional information: Object reference not set to an instance of an object.

What can I do now?
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