properly dealing with null database values in vb.net

Question

I am looping thorugh a datatable and and printing each row to the console and I keep on getting a dbnull error. I inserted an if statement in my loop to try and catch it, but I can't seem to get it to work. Any ideas?

Thanks!

                Do While reader.Read
                For i As Integer = 0 To reader.FieldCount - 1

                    If reader.IsDBNull(i) Then
                        Console.Write(Nothing)
                    Else
                        Console.Write(reader.GetString(i))
                    End If

                Next
                Console.WriteLine(Environment.NewLine())

Check if you are really getting a DBNull error and post it.

Olaf
– Olaf

2012-01-01 16:45:36 +00:00
Commented Jan 1, 2012 at 16:45 — Olaf
– Olaf, Commented Jan 1, 2012 at 16:45

Olaf · Accepted Answer · 2012-01-01 16:45:29Z

2

Changing Console.Write(Nothing) to Console.Write("Nothing") might remove one error, and reader.GetString(i) might throw InvalidCastException errors - you should catch this. reader.IsDBNull(i), however, looks correct.

answered Jan 1, 2012 at 16:45

Olaf

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1 Comment

Lance Collins Over a year ago

Yeah, it didn't like the write(nothing). I ended up just putting " , " as the string and it works fine now.

Robert Beaubien · Accepted Answer · 2012-01-01 16:59:16Z

1

I have never used the reader methods, but Console.Write(Nothing) would likely have issues. Try this:

        Do While reader.Read
        For i As Integer = 0 To reader.FieldCount - 1

            If reader.Item(i) Is DBNull.Value Then
                Console.Write("")
            Else
                Console.Write(CStr(reader.Item(i)))
            End If

        Next
        Console.WriteLine(Environment.NewLine())
    Loop

answered Jan 1, 2012 at 16:59

Robert Beaubien

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Comments

logixologist · Accepted Answer · 2012-01-01 17:04:35Z

1

Why not simply change it to

        If NOT isdbnull(reader.Item(i)) Then
            Console.Write("")
        Else
            Console.Write(CStr(reader.Item(i)))
        End If

That has always worked better for me. I dont know if there is a DBNull vs DBNull.value issue here.

answered Jan 1, 2012 at 17:04

logixologist

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