In my database on my SQL Server I have a table with users. This table have a column named logged_on which is a bit, either true or false. When someone log on the column will be true, else false. If something ever happens when someone is using my wpf-application, like the power disappears and the application couldn't log out the user this column will be true and the user will not be able to login again, because the application will tell this user that he is already logged on. Is there something i could do to avoid this situation? On the server-side or in the application?
Any sugestions are appreciated :)
I think you'll need a "LastActive" date-time stamp. Then run a scheduled job that says "if you've been inactive for X minutes, change the state of the logged_on flag".
Are you trying to insure that only one login can be active at the same time? Is that the end game?
Sounds like you need to change the approach a little, perhaps tracking last interaction date/time (every time the WPF app calls SQL) and enforcing a session timeout limit instead. You could use that DateTime to automatically log out anyone that hasn't interacted with the server in several minutes by checking it in addition to the *logged_on* bit field (always switching *logged_on* to false if the DateTime is too stale).
Is there an important reason you can't just throw away the old login in situations where the user logs in again without logging out first?
Related
IDE: Visual Studio, C# .net 4.0, Winforms application
Is there any way in SQL Server to implement a column in a table which can set itself automatically to 0 when it has not received any ACK (acknowledgement) signal from the application side?
The requirement is I want to keep a column which can keep track that Is application is open or it has been closed?
One way to implement is using the OnClose() event, i.e. on Close() I can change it's value to 0. but the problem is suppose application got hanged for some reason or Power is gone than the value in database will not be updated to zero.
So I want to create an automated column which can track this situation and make itself zero when the application is not sending any request or idle means closed.
please suggest how to handle this.
You can't do that. The only thing you can do is to save GETDATE() in a column in a table as the last activity time of the application and invoke the stored procedure from a high-priority thread every 10 seconds for example.
When you want to know if the application is alive or not, just check this value, if more than 10 seconds is passed since then, you app is gone.
UPDATE:
A more precise but complex approach would be to listen on a socket inside your application and then whenever you want to know if the application is alive, send a request from your sql script to PING the application. You should use CLR programming for this approach, but I think the first one will be practically enough.
Considering it will be a multiple instance scenario where multiple instances of the application can point to same database. You can try the following:
Create a separate table to maintain sessions. This table would contain three columns 1)Machine name or IP 2) Session Id (GUID) and 3) TimeStamp.
Whenever application starts create a new session id and make an entry into this table it means new session is started.
Keep on updating timestamp on every request based on session id.
Have a timeout configured somewhere in web.config or database which will come in handy later.
Now when application is exiting gracefully then delete the row from the table.
Now if application crashes the row won't be delete so next time when application starts you can check if the row already exists. Use machine name or IP to query to the table.
Use the timeout setting configured in (3) above to determine since how long the application is idle.
I build web-site and want to count clicks on some button. I create and try this class of counter:
public static class Counter
{
public static int counter = 0;
}
Every time I click on the button the counter is increament (counter++) ans I see it in my site, But, if I close the chrome and enter again to my site the counter starts from zero.
How can I save the counter? "Static" dont need to do that?
My bet is that it happens because the application space is flushed - it shouldn't reset just because you closed your browser window, thus abandoning the current session (if the session cookie isn't persistent, that is.)
Visual Studio may republish your files (if using a remote IIS) or just plainly restart a local IIS Express instance, depending on how you set your development environment; I do believe setting a specific content as Static would cause it to be available to all current sessions.
That said, you may want to keep it under the current session (using the Session object).
Optionally, if you want to persist information in between server restarts, you may try reading and writing to a local storage, such as a plaintext or XML file. You can find a very nice article about this on the following link:
http://www.codeproject.com/Articles/544839/Implement-ASP-NET-custom-XML-file-configuration
A more sophisticated version would use a local (or remote) database, for example.
Hope it works for you.
static fields are unique per-process. Depending on your application pool configuration, you could have 2, 20 or 100 copies of that.
They're also not thread safe. There are very, very few instances (pun) where a static member is appropriate.
Just off the top of my head, a particular "instance" of a static will disappear when:
The application pool is recycled. On IIS, this defaults to 20 minutes of inactivity.
The application process exits (you may have multiple processes running within your app pool). This happens as part of (1), but will also happen if, say, you're using the Visual Studio debug web server (Cassini), have your project configured to launch the site for debugging, and close the browser that was launched initially. (This happens because VS considers closing the browser that it launched equivalent to saying "I'm done playing. Back to coding now," or hitting the stop button.)
Another thread overwrites the value you've stored (google "race condition.")
You really, really should be storing this in a database. If you're building a website, you need a database anyway. ANYTHING related to application state should be stored in the database.
ALSO, this really, really shouldn't be happening server-side. Are you really performing a postback every time someone clicks anywhere on a page? If so, you have JavaScript in place to handle that, so just skip this insanity, have said script fire off an AJAX request, and have the target handler log it in the database.
Looks like your using a web site so presuming ASP.net. There are a number of ways to store the information. Database could be one or a persistent cookie could be the way to do it. See this article on how to create cookies: How do I set/unset cookie with jQuery?
You can try save it in session and then it will stay until the session is time out(20 minutes) if you want it to long time just write it to file in known location and when you close the web write the value to the file and when the web is up again take the vakue from the file.
I have a desktop C# application, several clients are connected into SQL server. Each user has an ID and Password. what do i want is to prevent an already logged-in user to log-in from another computer.
I have implemented it by updating a Field in the database 'UserLoggedIn'=true at the login, and when the user logs out the Field Updated into False. But this solution is not optimal, in which if the system crashed or the computer shutdown unexpectedly, the value will stay 'UserLoggedIn'=True in the database and this user will never can log-in again to the system.
What is the optimal solution for that, and prevent an already logged-in user from logging-in from another computer?
Instead of true, store a timestamp in the database. Make sure that you update it periodically while the user is logged in.
When they log in, allow them if it's not too new. That is: if you've seen them from another PC within the last (say) 30 seconds, then consider that session still live, and reject the new login.
This way, if their other PC crashes, the timestamp will not be updated, and will eventually expire.
The update frequency should be about twice the expiry timeout. For example, if you want a session expiry of 1 minute, you should update the timestamp every 30 seconds.
I would suggest that you check if the user has already established a connection to the database using the following query
SELECT loginame as LoginName,program_name
FROM sys.sysprocesses
WHERE db_name(dbid)='my_database' and loginame='test_user'
If the number of records returned is greater than zero then you can assume that a user has already connected to the database from your application.
If you look at the connection string property in MSDN, you will find the following properties of interest. These 2 properties can be added to your existing connection string to further improve the filters that can be defined in the query above
Application Name - The name of the application, or '.Net SqlClient Data Provider' if no application name is provided. (=program_name in the table above)
Workstation ID - The name of the workstation connecting to SQL Server. (=hostname in the table above )
I believe that this solution will work irrespective of crashes on the client side and does not require that you save the state in any table.
This might be a silly question but i was wondering if it would be a good idea to delete all expired "sessions" from my database, every 15 minutes?
Or just leave it there? Session expires after X minutes, its no longer useful anymore, seems like it just taking up space?
When my team deploys SQL Server session state in a .NET application, we simply create a job with SQL Server Agent to clean up the expired sessions nightly (or at some appropriate interval).
Unless you have massive amounts of traffic, you can do this whenever it is convenient without worrying about instantly deleting unused sessions, but it's definitely a good idea to clean up.
If you're using the standard SQL Server Session State, old sessions are automatically deleted for you. Until the old entries are deleted, sessions do not expire, since the provider does not actively monitor the Expires column in the session table.
The install / configuration utility creates a SQL Agent job that calls the DeleteExpiredSessions stored procedure every 60 seconds. This means that SQL Agent needs to be running for session expiration to work and for the table to get cleaned up.
If your table looks like that
SessionId datatype,
SessionLastTouch datetime
then when registering the new session do some cleanup after writing(session issue or touch) to the table, like this:
delete from YourSessionsRegister WHERE SessionLastTouch < DATEADD(min, -15, GETDATE())
BUT
May be better way is to cleanup the session register based on some schedule - to reduce DB load in peak hours - simply create the job, which cleans up the register every night or smth. like this
HI All,
i wish begin to work about a feature new for me ,i'n my project i have a database( with SqlServer) and an application (developing in WPF) the purpose of this application is to manage/handle about Accountancy and other Departement,so i created a Passwords and Roles(for Users) to access in the application ,now i will create a system to knows how many Usera are connected to the Application(via Database )and show that in a listBox(for example like a normal Chat Application i wish knows who is online and offline) but i don't know where i need begin to work out this feature ,i'm strange to this feature so if you have any suggestion,link and else i will appreciate so much your help.
Thanks so much.
P.S. if my question is not clear i will rewrite it...however sorry in anticipate
Without knowing the details of your application, I would suggest setting a timestamp field in the database when they log in, and then set it again every X minutes while they are logged in. This has two advantages over just setting a flag:
1) If the application crashes, or the user's machine crashes, the flag will not be reset, and you will have no way of knowing that they are not still logged in.
2) The timestamp will tell you the last time each user was logged in, even if they are not logged in currently.
Maybe in the database itself? When the user logs in, you can set a flag for each user "LoggedInd = true", and when they log out "LoggedIn = false". And do a query on that flag "SELECT * FROM Users WHERE LoggedIn = true"