Who is online ASP.NET (Sessions tutorial)

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Ok, here is a code snipet to determine who is online on your web site.
Essentially there are 2 tables Users and OnlineUsers. I did it this way to not attach the 
sessionID field to each user (text about 20 chars long) and waste DB space.
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the UserID can be autonumeric (PK) .
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First of all, when a user log in, we insert a record on the OnlineUsers table. The values 
are the UsserID that loged in (duh) and the sessionID property of the Session Object.
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Here is a code snippet: (for the login form, assuming you are using forms authentication)
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Private Sub LoginButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) 
Handles LoginButton.Click <br>
Response.cookies(“UserID”)=txtUsername.Text <br>
Dim cnn as new oledb.oledbconnection(ConfigurationSettings.Appsettings(“cnnString”)<br>
Dim strInsert as string = “Insert into OnlineUsers (UserID,SessionID) Values(‘ “ & 
txtUserName.Text & “’,’” & Session.SessionID & “’)” <br>
Dim oldbInsert as new oledbCommand(strInsert,cnn)<br>
Cnn.open()<br>
OldbInsert.ExecuteNonQuery()<br>
Dim strUpdate as string = “Update Users set Online = True where UserID =’“ & 
txtUserName.Text & “’” <br>
Dim oldbUpdate as new oledbCommand(strUpdate,cnn)<br>
OldbUpdate.ExecuteNonQuery()<br>
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End Sub<br>
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Now, when the users click logout somewhere in your page:<br>
<br>
Private Sub LogoutButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) 
Handles LogoutButton.Click<br>
<br>
Dim cnn as new oledb.oledbconnection(ConfigurationSettings.Appsettings(“cnnString”)<br>
Dim strDelete as string = “Delete from OnlineUsers where SessionID =’” & Session.SessionID & 
“’” <br>
<br>
Dim oldbDelete as new oledbCommand(strdelete,cnn)<br>
Cnn.open()<br>
OldbDelete.ExecuteNonQuery()<br>
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<br>
Dim strUpdate as string = “Update Users set Online = false where UserID =’“ &  
Response.cookies(“UserID”).value & “’” <br>
Dim oldbUpdate as new oledbCommand(strUpdate,cnn)<br>
OldbUpdate.ExecuteNonQuery()<br>
<br>
End Sub
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Now, what for am I using the session ID?<br>
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What happens if a user doesn’t press the logout button? It will be online until it hits the 
logout button.<br>
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So in your Session_End event. In your Global.asx.vb you can put this code so when the 
session expires, the app automatically deletes the record from the users table and put the 
online status = False.<br>
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Sub Session_End(ByVal sender As Object, ByVal e As EventArgs) <br>
<br>
 Dim cnn As New<br> 
OleDb.OleDbConnection(ConfigurationSettings.AppSettings("ConnectionString") & 
ConfigurationSettings.AppSettings("DBPath")) <br>
 Dim strUserID As String = "" <br>
 Dim rdr As OleDb.OleDbDataReader <br>
 Dim com As New OleDb.OleDbCommand("Select UserID from OnlineUsers where SessionID 
='" & Session.SessionID & "'", cnn) <br>
<br>
 cnn.Open() <br>
 rdr = com.ExecuteReader <br>
 While rdr.Read() <br>
  strUserID = CStr(rdr.GetValue(0)) <br>
 End While <br>
 rdr.Close() <br>
 If strUserID <> "" Then <br>
  com.CommandText = "Delete from OnlineUsers where UserID =" & strUserID <br>
  com.ExecuteNonQuery() <br>
  com.CommandText = "Update Users Set Online = False where UserID =" & strUserID 
<br>
  com.ExecuteNonQuery() <br>
 End If <br>
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 cnn.Close() <br>
 End Sub<br>
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Now you can present the users with the Online=true on a datagrid or other bound control =)
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Note:<br>
You cannot call subs or functions from the session_end events, or it will not execute.<br>
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Also When an error occurs you don’t get notified, even in debug, because this is executed in 
a background process.<br>
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So I hope you learn a little from this tut, I passed long hours to get to this =)<br>
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And a final note: sorry about my English, I’m from Mexico (heheh)<br>
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Vote!