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VB Databases Basics Beginning-level VB coding questions specific to using VB with databases. Issues not specific to database use will be redirected to other forums.
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Old June 16th, 2003, 01:51 PM
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Default Updating Unique Identifier foreign key to NULL

I have a VB front-end/SQL Server backend form with a combobox on it. The combobox updates a record with a field in it that is a foreign key to another table, with datatype of uniqueidentifier. It works fine if there is a value selected in the combobox. If there is not, I get an error:

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

Additional information: Invalid cast from Microsoft.VisualBasic.VariantType to System.Guid.

How can I insert a null into my sql table?



Here is the relevant code:

Private Sub UpdateRecord()
        Dim intPosition As Integer
        Dim objCommand As SqlCommand = New SqlCommand()
        Dim sqlParm As New SqlClient.SqlParameter()

        intPosition = EventCM.Position
        objCommand.Connection = EventsCon
        objCommand.CommandText = "UPDATE vwEvents SET Fuel = @Fuel WHERE EventID = @EventID"
        objCommand.CommandType = CommandType.Text

        sqlParm = objCommand.Parameters.Add("@Fuel", SqlDbType.UniqueIdentifier)
        If Fuel.SelectedIndex = -1 Then
            sqlParm.Value = VariantType.Null
            sqlParm.Value = Fuel.SelectedValue
        End If
        objCommand.Parameters.Add("@EventID", BindingContext(EventDV).Current("EventID"))
        Catch e As SqlException
            MsgBox(e.Message + e.ToString)
        End Try


        EventCM.Position = intPosition
End Sub
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