VB.NET中的autoNumber

Question

i want to migrate from VB6 to VB.NET, but still rookie. how to make autoNumber procedure works like code in VB6 in VB.NET (VB2012), below my code so far.

below my previous code in VB6, this code will work when addbutton_click, it will display CDEUSR005, since there are 4 record in table before, CDEUSR001, CDEUSR002, CDEUSR003, CDEUSR004. Image sample that works in VB6

Sub autoNumber()
    Rs_User.Requery
    Set Rs_User = New ADODB.Recordset
    strSQL = "SELECT userCode FROM tblUser ORDER BY userCode"
    Rs_User.Open strSQL, Conn, adOpenDynamic, adLockBatchOptimistic
    If Rs_User.BOF Then
        NewCode = "CDEUSR001"
        Exit Sub
    Else
        Rs_User.MoveLast
        NewCode = Rs_User!userCode
        userCode = Right(userCode, 3)
        userCode = Val(userCode) + 1
        If Len(userCode) > 5 Then
            Exit Sub
        End If
    End If
    userCode = "CDEUSR" & Format(NewCode, "000")
 End Sub

this is my VB.NET(VB2012) code, when the add button, it will show CDEUSER001, not display CDEUSR005. Image sample that wont' works in VB.NET

Sub autoNumber()
    sql = New Odbc.OdbcCommand("SELECT userCode FROM tblUser ORDER BY userCode", conn)
    dr = sql.ExecuteReader
    dr.Read()

    If (xxxx which has same function with Rs_User.BOF) Then
        NewCode = "CDEUSR001"
        Exit Sub
    Else
        NewCode = Microsoft.VisualBasic.Right(dr.GetString(0), 3)
        NewCode = Val(NewCode) + 1
        If Len(NewCode) > 5 Then
            Exit Sub
        End If
    End If
    NewCode = "CDEUSR" & Format(NewCode, "000")
End Sub

Answer 1

The difference between ADODB in VB6 and OdbcConnection in VB.NET is that OdbcConnection often uses OdbcDataReader.HasRows property as ADODB.Recordset.BOF or ADODB.Recordset.EOF counterpart.

Your VB.NET code should be modified as this ( Using block added as common convention when initializing OdbcConnection ):

Sub autoNumber()
    Using conn As New OdbcConnection(...)
        Using sql As New OdbcCommand("SELECT userCode FROM tblUser ORDER BY userCode", conn)
           Using dr As OdbcDataReader = sql.ExecuteReader()

               ' similar like Recordset.EOF or BOF
               If dr.HasRows = False Then 
                   NewCode = "CDEUSR001"
                   Exit Sub
               Else
                   dr.Read()
                   ' dr("userCode") may also work here
                   NewCode = Right(dr.GetString(0), 3)
                   NewCode = Val(NewCode) + 1
                   If Len(NewCode) > 5 Then
                      Exit Sub
                   End If
               End If
            NewCode = "CDEUSR" & Format(NewCode, "000")
            End Using
        End Using
    End Using
End Sub

Note: Unlike ADODB.Recordset , OdbcDataReader doesn't have row indexing to determine last row, but DataSet does. You can retrieve the last record in DataSet as given below:

Dim ds As DataSet = New DataSet()

Using conn As New OdbcConnection(...)
   Using sql As New OdbcCommand("SELECT userCode FROM tblUser ORDER BY userCode", conn)
       Dim adapter As OdbcDataAdapter = New OdbcDataAdapter(sql)
       adapter.Fill(ds)

       ' here to get last row from DataSet
       ' related: stackoverflow.com/questions/2099379/
       NewCode = Right(ds.Tables(0)(ds.Tables(0).Rows.Count - 1)("userCode"), 3)

       ' other stuff

   End Using
End Using