Caution ADO and ADO MD have not been fully tested in a Microsoft .NET Framework environment. They may cause intermittent issues, especially in service-based applications or in multithreaded applications. The techniques that are discussed in this article should only be used as a temporary measure during migration to ADO.NET. You should only use these techniques after you have conducted complete testing to make sure that there are no compatibility issues. Any issues that are caused by using ADO or ADO MD in this manner are unsupported. For more information, see the following article in the Microsoft Knowledge Base:
840667 (http://support.microsoft.com/kb/840667/) You receive unexpected errors when using ADO and ADO MD in a .NET Framework application
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SYMPTOMS
On a computer that has Microsoft .NET Framework 1.0
installed (and that does not have Microsoft Visual Studio .NET installed), when you try to
access data using ADO Interop on an ASP.NET page that resides at an identical site
and that is hosted on the same computer, you may receive the following error
message:
Exception Details:
System.NullReferenceException: Object reference not set to an instance of an
object.
To resolve this problem, register the Adodb.dll file in the
global assembly cache (GAC). On a computer where only the .NET Framework is
installed, the file Gacutil.exe does not exist.. Either obtain the gacutil file
by installing Microsoft .NET Framework SDK, or create a Visual Studio.NET setup
project that uses the installer to install the correct components.
To
register Adodb.dll in the GAC, follow these steps:
1.
Click Start and then click
Run.
2.
In the Run dialog box, type the following
command, and then click OK:
Create a new Microsoft Visual C# project named ADORefError.
By default, WebForm1.aspx appears.
2.
On the Project menu, click Add
Reference.
3.
On the .NET tab, select adodb from the drop-down list.
4.
Click Select, and then click
OK.
5.
Drag a Label control from the toolbox to WebForm1.aspx.
6.
In Solution Explorer, right-click
WebForm1.aspx, and then click View
Code.
7.
Paste the following code in the Page_Load event:
Note You must change the User Id <user
name> value to an account that has the appropriate permissions to perform
these operations on the database.
//Create ADODB Objects
ADODB.Connection oConn = new ADODB.ConnectionClass();
ADODB.Recordset oRS = new ADODB.RecordsetClass();
//Change Connection String depending on your SQL Server
string strConn = "Provider=SQLOLEDB.1;Persist Security Info=False;User ID=<username>;Initial Catalog=pubs;Data Source=Your SQLServer Name";
oConn.Open(strConn,"","",0);
object objRecs = 100;
oRS = oConn.Execute("select au_Id, au_lname from authors", out objRecs,0);
//Error is generated by referencing the Fields collection
Label1.Text = oRS.Fields["au_id"].Value.ToString();
//Close all connections
oRS.Close();
oConn.Close();
//Release COM Objects
oRS = null;
oConn = null;
8.
Copy Adodb.dll (from the C:\Program
Files\Microsoft.NET\Primary Interop Assemblies\ folder) to the Bin folder of
the ADORefError application.
9.
On the Build menu, click Build
Solution.
10.
Start Microsoft Internet Explorer, and then browse to
WebForm1.aspx by specifying the following URL, where
IISServerName is the name of your Microsoft Internet
Information Services (IIS) server:
http://IISServerName/ADORefError/WebForm1.aspx
11.
Identify a test computer that has the .NET Framework
installed (without Microsoft Visual Studio .NET). In IIS, create two virtual
directories and name them Test1 and Test2.
12.
Create two identical sites: from the ADORefError folder,
copy WebForm1.aspx and the Bin folder to the Test1 and Test2 folders on the
test computer.
13.
Start Microsoft Internet Explorer and browse to
WebForm1.aspx of Test1 site by specifying the following URL, where
IISServerName is the name of your Microsoft Internet
Information Services (IIS) server:
http://IISServerName/Test1/WebForm1.aspx
14.
Start another instance of Microsoft Internet Explorer and
browse to WebForm1.aspx of Test2 site by specifying the following URL:
http://IISServerName/Test2/WebForm1.aspx
15.
When you access WebForm1.aspx of Test2, you receive the
error message as detailed in the SYMPTOMS section.
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