使用服务器路径在vb.net中登录 [英] login in vb.net using server path

问题描述

我想使用服务器路径登录。但是我无法做到。

i want to login using server path. But i am not to able to.

Dim con As New OleDb.OleDbConnection
        Dim dbProvider As String
        Dim dbSource As String
        '   Dim info As DirectoryInfo = New DirectoryInfo("App_Data\CM.mdb")

        dbProvider = "PROVIDER=Microsoft.Jet.OLEDB.4.0;"
        dbSource = HttpContext.Current.Server.MapPath("/App_Data/CM.mdb")

        con.ConnectionString = dbProvider & dbSource
        con.Open()

        MsgBox("Database is now open")

        con.Close()

        MsgBox("Database is now Closed")

i收到错误消息，表示已处理Null Reference Exception。



Plz帮助..



问候，

Megha

i am getting an error saying Null Reference Exception was handled.

Plz help..

Regards,
Megha

推荐答案

第一个问题：您的连接字符串无效。您在提供程序和数据库路径之间缺少 Data Source = 。

http://www.connectionstrings.com/access/ [ ^ ]





第二个问题：您的数据库路径将仅当您的应用程序位于站点的根目录时才起作用。改为使用app相对路径：

First problem: Your connection string is invalid. You're missing a Data Source= between the provider and the database path.
http://www.connectionstrings.com/access/[^]


Second problem: Your database path will only work if your application is at the root of a site. Use an app-relative path instead:

dbSource = HttpContext.Current.Server.MapPath("~/App_Data/CM.mdb")

第三个问题：在ASP.NET应用程序中调用 MsgBox 将无法正常工作。如果你很幸运，你会得到一个异常，表明当前进程不是交互式的。如果没有，你会弹出一个消息框在服务器上，没有人会看到它，你的代码将等待有人点击确定。



第四个问题：你实际上没有显示或描述你的代码是如何被调用的，或是异常被抛出的那一行，但我猜你是尝试在 HttpContext.Current 不可用时调用代码。尝试将 MapPath 行更改为：

Third problem: Calling MsgBox in an ASP.NET application will not work. If you're lucky, you'll get an exception indicating that the current process isn't interactive. If not, you'll pop up a message box on the server, where nobody will ever see it, and your code will hang waiting for someone to hit "OK".

Fourth problem: You haven't actually shown or described how your code is called, or what line the exception is thrown from, but I'm guessing that you're trying to call the code at a point when HttpContext.Current is not available. Try changing the MapPath line to:

dbSource = System.Web.Hosting.HostingEnvironment.MapPath("~/App_Data/CM.mdb")

编辑：根据评论，此代码适用于 Windows 应用程序，而不是ASP.NET应用程序。



Windows应用程序没有当前的 HttpContext 。 HttpContext.Current 将始终返回 Nothing 。当您尝试访问 HttpContext.Current.Server 时，它将始终抛出 NullReferenceException 。



此外，Windows应用程序没有 App_Data 文件夹。



您需要为访问数据库指定正确的文件系统路径。假设数据库文件与应用程序位于同一文件夹中，您可以使用 | DataDirectory | 作为快捷方式：

As per the comment, this code is for a Windows application, not an ASP.NET application.

Windows applications do not have a current HttpContext. HttpContext.Current will always return Nothing. When you try to access HttpContext.Current.Server, it will always throw a NullReferenceException.

Furthermore, Windows applications don't have an App_Data folder.

You will need to specify the correct file-system path to your access database. Assuming the database file is in the same folder as your application, you can use |DataDirectory| as a shortcut:

Dim con As New OleDb.OleDbConnection
Dim connectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=|DataDirectory|\CM.mdb;Persist Security Info=False;"

con.ConnectionString = connectionString
con.Open()

MsgBox("Database is now open")

con.Close()

MsgBox("Database is now Closed")

注意：运行应用程序的用户将会要求对包含数据库文件的目录进行写访问。

NB: The user running your application will require write access to the directory containing the database file.

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