Bug #56918 Reader.getstring fails on null value

• Submitted: 22 Sep 2010 7:04
• Modified: 22 Sep 2010 7:32
• Reporter: Olivier Olivier
• Status: Closed
• Category: Connector / NET
• Severity: S2 (Serious)
• Version: 6.2.4
• OS: Windows
• CPU Architecture: Any

[22 Sep 2010 7:04] Olivier Olivier

Description:
Hi, 

I want to find max value from a table with a sql query like "Select max(id) from <table>;" My problem is that when the table is empty, this query returns one row with max='null'. So reader.read is true when reader.getstring(0) generates error. I tried to test isdbnull(reader.getstring(0)) but the error is still generated.

Am I doing wrong ? Is there another way of doing that ?

Thanks.

How to repeat:
        Try
            Dim cmd As New MySqlCommand(sql, cnx)
            Dim reader As MySqlDataReader
            reader = Nothing
            reader = cmd.ExecuteReader()
            If reader.HasRows Then
                reader.Read()
                If IsDBNull(reader.GetString(0)) Then ' Catch on "reader.getstring")
                    id = "0"
                Else
                    id = reader.GetString(0)
                End If
            End If
            If Not reader Is Nothing Then reader.Close()
        Catch ex As Exception

[22 Sep 2010 7:16] Olivier Olivier

Mistake. Right syntax is 

If reader.HasRows Then
                reader.Read()
                If reader.IsDBNull(0) Then
                    id = "0"
                Else
                    id = reader.GetString(0)
                End If
            End If