Question

在表单上运行以下代码时，我收到上述错误消息

 Dim SqlString As String = "select [containmentid],[incidentid],[containmentdate],[containment] from [containment] WHERE [incidentid] = " & lbl_incidentid.Text & ""
    Using conn As New OleDbConnection(ConnString)
        Using command As New OleDbCommand(SqlString, conn)
            Using adapter As New OleDbDataAdapter(command)
                conn.Open()
                Dim reader As OleDbDataReader = command.ExecuteReader()
                Try
                    If reader.Read() Then
                        Button1.Visible = False
                    Else
                        Button1.Visible = True
                    End If
                Finally
                    reader.Close()
                End Try
            End Using
        End Using
    End Using

我以为是因为我在lbl_incidentid部分周围缺少一个叛逆者，所以如果我修改sql行来阅读

Dim SqlString As String = "select [containmentid],[incidentid],[containmentdate],[containment] from [containment] WHERE [incidentid] = '" & lbl_incidentid.Text & "'"

我现在收到以下错误

标准表达式中的数据类型不匹配。

如果我修改sql行来读取一个我知道的数字，如下所示

 Dim SqlString As String = "select [containmentid],[incidentid],[containmentdate],[containment] from [containment] WHERE [incidentid] = 622"

它工作正常，我一定会错过一些明显的东西，但我无法看到它。谁能告诉我为什么我的代码错了？

Answer 1

也许您需要删除整数周围的撇号。但是，不要试图解决这个问题。而是始终使用sql-parameters。例如，为了防止sql-injection：

Dim SqlString As String = "select [containmentid],[incidentid],[containmentdate],[containment] from [containment] WHERE [incidentid] = @incidentid"
Using conn As New OleDbConnection(ConnString)
    Using command As New OleDbCommand(SqlString, conn)
        ' *** That's all you need to safeguard your code: ***
        command.Parameters.Add("@incidentid", OleDbType.Integer).Value = CInt(lbl_incidentid.Text)
        Using adapter As New OleDbDataAdapter(command)
            conn.Open()
            Dim reader As OleDbDataReader = command.ExecuteReader()
            Try
                If reader.Read() Then
                    Button1.Visible = False
                Else
                    Button1.Visible = True
                End If
            Finally
                reader.Close()
            End Try
        End Using
    End Using
End Using

没有为一个或多个必需参数读取器vb.net给出的值

1 个答案: