Updating db table field based on user activity using windows application c#

Question

I have created one project in windows application and I provided multiple users accessibility for the project but I need restrict it to only 3 users accessing it at a time. For that purpose I have added column status (bit), for every login I made status=true and log out status=false but if I ended my project from end task and system shutdown then I'm getting problem in counting logged users.

Is it possible to find active users and there status? If it is possible then I'll run trigger every 5 minutes and update the status fields accordingly.

Answer 1

OK, so since this is a Windows application, and you haven't provided any code, I'd do something like this when they login:

// connect to the database
using (SqlConnection c = new SqlConnection("connection string"))
{
    // count the logged in users
    var loggedInUsers = (int)new SqlCommand("SELECT COUNT(UserId) FROM Users WHERE status = 1", c).ExecuteScalar();

    // if the threshold has been met then shut down the application
    if (loggedInUsers == 3)
    {
        MessageBox.Show("There are already 3 concurrent users logged into the system -please try again at a later time.", "User Limit Met", MessageBoxButtons.OK, MessageBoxIcon.Information);
        Application.Exit();
    }
}

but you also have to do this when the application shuts down, like in the OnClosing method of the main form:

protected override void OnClosing(CancelEventArgs e)
{
    // connect to the database
    using (SqlConnection c = new SqlConnection("connection string"))
    {
        // log the user out
        var cmd = new SqlCommand("UPDATE Users SET status = 0 WHERE UserId = @UserId", c);
        cmd.Parameters.AddWithValue("@UserId", // get your user id from somewhere

        var rowsAffected = cmd.ExecuteNonQuery();

        // make sure the update worked
        if (rowsAffected == 0)
        {
            // do something here to make sure they get logged out
        }
    }
}

EDIT

To handle the edge case of an application failure during a task manager quit for example you should be able to leverage Application.Exit , so in your startup method (ie where Application.Run is called) put this line before that:

Application.ApplicationExit += new EventHandler(Application_ApplicationExit);

and then consume it:

private void Application_ApplicationExit(object sender, EventArgs e)
{
    // and now you can probably just move all of the code here
    // instead of the OnClosing
}