Question

我有这个vb.net代码：

conn6.ConnectionString = "server=" + global_variables.web_server_ip + "; user id=" + global_variables.web_server_username + "; password=" + global_variables.web_server_password + "; database=" + global_variables.web_server_database + "; "
conn6.Open()

SQL = "select calltype from billing group by calltype "
myCommand6.Connection = conn6
myCommand6.CommandText = SQL

reader6 = myCommand6.ExecuteReader

While reader6.Read
    cdr_call_type = reader6.GetString(0)
                    ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
    'do VoIP bit
                    ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
    If customerid_voip <> "" Or customerid_voip_new <> "" Then
       'do customer VoIP Bit, which means getting the latest value from billing table 
       TextBox1.Text = "Got VoIP - " + cdr_call_type + vbCrLf + TextBox1.Text
       Me.Refresh()

       conn3.ConnectionString = "server=" + global_variables.web_server_ip + "; user id=" + global_variables.web_server_username + "; password=" + global_variables.web_server_password + "; database=" + global_variables.web_server_database + "; "
       conn3.Open()

       SQL = "select reseller_bill, customer_bill, phone, calltype, timestamp, seconds from billing where calltype = '" + reader6.GetString(0) + "' AND (source='CDR' or source='' or source='VOIP') and (company='" + customerid_voip + "' or company='" + customerid_voip_new + "') "
       myCommand3.Connection = conn3
       myCommand3.CommandText = SQL

       reader3 = myCommand3.ExecuteReader

       While reader3.Read
          'do stuff here
       End While

       reader3.Close()
       conn3.Close()
   End If
End While

reader6.Close()
conn6.Close()

当我运行代码时，我在行conn3.Open()上收到错误说：

连接时（state = Open），不允许更改'ConnectionString'属性。

它适用于第一个循环，但当我到达第二个循环时，它会停止并显示此错误

Answer 1

在修改之前，您可以添加一些额外的检查：

If conn3.State = ConnectionState.Open Then 
    conn3.Close()
End If

Answer 2

问题在于此while loop您正在尝试更改已定义连接的connectionString，可以通过每次在循环内创建新连接来避免此问题，如下所示：

   While reader6.Read
   cdr_call_type = reader6.GetString(0)
   If customerid_voip <> "" Or customerid_voip_new <> "" Then
       TextBox1.Text = "Got VoIP - " + cdr_call_type + vbCrLf + TextBox1.Text
       Me.Refresh()
       Dim conn3 As New OdbcConnection '<--- declaring a new connection
       '<---- in each iteration connection is treated as a new one
       '<---- so initializing is not became a problem
       conn3.ConnectionString = "server=" + global_variables.web_server_ip + "; user id=" + global_variables.web_server_username + "; password=" + global_variables.web_server_password + "; database=" + global_variables.web_server_database + "; "
       conn3.Open()
       '<------
       ' Remaining codes comes here
       '<------
    End IF

不允许更改ConnectionString

2 个答案: