Question

我是vb.net的初学者，当我开始编码错误“System.Data.dll中发生类型'System.InvalidOperationException'的未处理异常时”我不知道该怎么做。这是我的代码。

    Dim cmd As New OleDbCommand("SELECT * FROM [login] WHERE [ID] & [Password] =" & TextBoxUsername.Text & TextBoxPassword.Text & "", myConnection)

    myConnection.Open() '*its keep pointing at this* 

    Dim dr As OleDbDataReader = cmd.ExecuteReader
    Dim userFound As Boolean
    Dim userID As String = ""
    Dim UserPassword As String = ""
    While dr.Read
        userFound = True
        userID = dr("ID").ToString
        UserPassword = dr("Password").ToString
        Form2.Show()
        Me.Hide()
    End While
    If userFound = False Then
        MessageBox.Show("Invalid Username/Password")
        'Button","User Validation", MessageBoxButton.OK , MessageBoxIcon.Error)'
    End If
    myConnection.Close()
End Sub

结束班**

Answer 1

您目前还没有将参数包装在单引号中，并且您的WHERE子句语法似乎已关闭。你可能想要这样的东西：

"SELECT * FROM [login] WHERE [ID] = '" & TextBoxUsername.Text & "' AND [Password] = '" & TextBoxPassword.Text & "'"

这里一个更大的问题是你应该使用参数来构建你的查询，这不仅可以帮助你避免这样的问题，而且还可以帮助防止像SQL注入这样令人讨厌的事情：

' Build your connection ' 
Using(Dim myConnection As New OleDbConnection("{your-connection-string"}))
    ' Use parameters in your query '
    Dim query = "SELECT * FROM [login] WHERE [ID] = ? AND Password = ?"
    ' Build your command to execute '
    Using(Dim myCommand As New OleDbCommand(query, myConnection))
         ' Open your connection '
         myConnection.Open()
         ' Add your parameters (these will replace the ? in your query)
         myCommand.Parameters.AddWithValue("@ID",TextBoxUsername.Text)
         myCommand.Parameters.AddWithValue("@Password",TextBoxPassword.Text)
         Using(Dim myReader = myCommand.ExecuteReader())
              If myReader.HasRows Then
                   ' Do stuff '
                   userFound = True
                   userID = dr("ID").ToString
                   UserPassword = dr("Password").ToString
                   Form2.Show()
                   Me.Hide()
              Else
                   ' Do other stuff '
                   MessageBox.Show("Invalid Username/Password")
              End If
         End Using
    End Using
End Using

“System.Data.dll中出现未处理的'System.InvalidOperationException'类型的异常”Visual Studio vb.net使用数据库microsoft访问

1 个答案: