Question

我想从VB6迁移到VB.NET，但仍然是菜鸟。如何使autoNumber程序像 VB.NET中的VB6代码（VB2012），到目前为止我的代码下面。

在我之前的VB6代码下面，这个代码在addbutton_click时会起作用，它会显示CDEUSR005，因为前面有4条记录，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

这是我的VB.NET（VB2012）代码，当添加按钮时，它会显示CDEUSER001，而不是显示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

VB6中的ADODB与VB.NET中的OdbcConnection之间的区别在于OdbcConnection经常将OdbcDataReader.HasRows属性用作ADODB.Recordset.BOF或ADODB.Recordset.EOF对应项。

您的VB.NET代码应该被修改为这个（Using块在初始化OdbcConnection时作为通用约定添加）：

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

注意：与ADODB.Recordset不同，OdbcDataReader没有行索引来确定最后一行，但DataSet确实如此。您可以检索DataSet中的最后一条记录，如下所示：

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

VB.NET中的autoNumber

1 个答案: