login in vb.net using server path

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

VB

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 am getting an error saying Null Reference Exception was handled.

Plz help..

Regards,
Megha

Posted 28-Jul-14 23:09pm

megha sarath

Updated 28-Jul-14 23:16pm

Nirav Prabtani

v2

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megha sarath 29-Jul-14 5:39am

Plz help..

1 solution

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Richard Deeming · Answer 1 · 2014-07-29T06:27:00

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:

VB.NET

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

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:

VB.NET

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

EDIT: 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:

VB

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")

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