Trying to convert DBNull into a date without any luck so far.

Question

I am loading a value into a txtbox(driver) from our sql database using another a filled txtbox(car registration) as a filter.

So I will be able to get the right driver for that vehicle. As each vehicle can have a number of people driving it in its time, I am using an IIf clause to make sure the current driver is selected.

I am getting this error:

Operator '>' is not defined for type 'DBNull' and type 'Date'.

I know I need to convert the DBNull to a date format, but am struggling to do so, I have a tried a few things, and so far this is where I have got to.

            Dim cdriver As New Dictionary(Of String, Object)

        cdriver.Add("Registration", txtreg.Text)

        Dim currentdriver As DataTable

        currentdriver = BusinessData.VerifierLogic.Load("[Car History]", cdriver)

        Dim currentdrivername As String = ""
        Dim currentenddate As DateTime

        For Each row As DataRow In currentdriver.Rows
            If DateDiff(DateInterval.Day, row("end_date"), DateTime.Now) > 0 Then
                currentdrivername = row("driver_name")
                currentenddate = row("end_date")

                IIf(row("end_date") Is DBNull, "1 jan 1900", row("end_date"))
            End If
        Next

        txtdriver.Text = currentdrivername
    Catch ex As Exception

        MsgBox(ex.Message)

    End Try

Any help would be greatly appreciated

Paul

Answer 1

So row("end_date") is nullable? You can use the DataRow-extension method Field which supports nullable types and is strongly typed:

For Each row As DataRow In currentdriver.Rows
    Dim endDate As Date? = row.Field(Of Date?)("end_date")
    If endDate.HasValue AndAlso endDate.Value > Date.Now Then
       currentdrivername = row.Field(Of String)("driver_name")
       currentenddate = endDate.Value
       Exit For ' otherwise you are overwriting these variables always '
    End If
Next

Answer 2

Must Credit Tim Schmelter for his help.

I had to slightly change things to get it going but the meat of the code was yours. Here's the finished article:

            For Each row As DataRow In currentdriver.Rows
            Dim endDate As Date? = row.Field(Of Date?)("end_date")
            If Not endDate.HasValue Then
                currentdrivername = row.Field(Of String)("driver_name")
            ElseIf endDate.Value > Date.Now Then
                currentdrivername = row.Field(Of String)("driver_name")
            End If