Your way will work well Carl except in one case which may be a rare case
but not something to be neglected...
User A had a power failure while doing something urgent and he's unable
to restart his computer, so he borrows his colleague machine to continue his
task... In this case the application will not allow him to connect!
Leaving for home
See you tomorrow
Vahan
-----Original Message-----
From: [email protected] [mailto:[EMAIL PROTECTED] Behalf
Of [EMAIL PROTECTED]
Sent: Wednesday, June 08, 2005 3:50 PM
To: [email protected]
Subject: RE: [delphi-en] Re: Restrict only 1 terminal login for 1 user
The easiest way to restrict this is a two part system.
Part 1 restricts the terminal to one instance of the program. If the
program is already running, do not allow another session to start.
Part 2 checks to see of the user is in the ManageUsers table. If an entry
exists check the terminal value, if it is not the current terminal exit the
program.
-----Original Message-----
From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf
Of Vahan Yoghoudjian
Sent: Wednesday, June 08, 2005 10:24 AM
To: [email protected]
Subject: RE: [delphi-en] Re: Restrict only 1 terminal login for 1 user
John... what if the database runs 24/24? I think in SQL server there's a
table that shows you who has logged in, I'm not sure about
Firebird/Interbase tho...
Let's go back to Oracle, even if there's a table storing the login
information what happens again when there's a power failure... how does
Oracle solve this problem... Does it ping the terminal from time to time to
see if there's still a connection? does it force the user to disconnect
after some idle delay? what if this delay is not expired yet and the user
tries to reconnect from the same machine or from a different machine?
Vahan
-----Original Message-----
From: [email protected] [mailto:[EMAIL PROTECTED] On
Behalf Of John Dorlon
Sent: Wednesday, June 08, 2005 3:17 PM
To: [email protected]
Subject: RE: [delphi-en] Re: Restrict only 1 terminal login for 1 user
I have an idea, I don't know if it works in interbase or firebird, but it
works in Oracle.
In Oracle, there is a data dictionary (ie, system-owned) view that you can
query to see who is logged in. So if you have such a thing in your
database, query that in your login trigger.
Another idea (going back to adding login data to a table in a login
trigger) - at some point you asked "what happens if there is a power failure
- the data could get out of sync with the users?" To remedy this (if it's
possible) you could make a trigger run at database startup which would
delete all the rows from the table.
-----Original Message-----
From: [email protected] [mailto:[EMAIL PROTECTED]
Behalf Of Vahan Yoghoudjian
Sent: Wednesday, June 08, 2005 2:02 AM
To: [email protected]
Subject: RE: [delphi-en] Re: Restrict only 1 terminal login for 1 user
You can do two things here to prevent such cases
1) Specify a TimeOut delay that will 'disconnect' the user after a that
given period of idle time
2) Store also some information about the terminal... if a user is trying
to
login and his name is found in table ManageUsers and his terminal match
the
stored terminal information you should probably grant him access, but if
the
same user is trying to access from another terminal someone must be
messing
around probably... I know this isn't a good way to solve things but it is
a
way...
As for the point 1 it might help you a lot but not completely
Vahan
-----Original Message-----
From: [email protected] [mailto:[EMAIL PROTECTED]
Behalf
Of soonhuat ong
Sent: Wednesday, June 08, 2005 2:59 AM
To: [email protected]
Subject: Re: [delphi-en] Re: Restrict only 1 terminal login for 1 user
Hi,
Thanks for your comments. One more question here, when the user logout
from
the terminal, I'll delete it from the ManageUsers table. What about if
there's an electrical/power failure or other cause ?? That particular user
record won't deleted, so next time when he/she try to login the "Exception
TooManyLogins" will be executed. Thanks again.
Mick Arundell <[EMAIL PROTECTED]> wrote:
Message: 11
Date: Tue, 7 Jun 2005 00:40:37 -0700 (PDT)
From: soonhuat ong <[EMAIL PROTECTED]>
Subject: Restrict only 1 terminal login for 1 user
Is there any way for me to restrict that one user can
only allow to
login 1 terminal/PC . Means that if they try to login
to other PC, the
system will provide them with the message : "Login
failure". For your
information, i'm using Interbase 6. Thx
Soonhuat,
1) Drop Interbase 6 use Firebird
2) I assume you want to limit each user to one login
at a time.
Solution,
Create table ManageUsers(
UName char(32),
constraint ManageUsers_Pk primary key (Uname)
);
create Exception TooManyLogins 'Only one login at a
time';
set term ^ ;
create trigger ManageUsers_Bi for ManagerUsers
active
before insert
position 0
as
begin
new.UName = Current_User;
end
set term ; ^
On your datamodule have an sql object with the code
insert into ManageUsers
(UName)
values
('user') /* any value here since it will be replaced
by the trigger*/
in your client application have a routine that runs
after connect
procedure TDataModule.AfterDbConnect(Sender : TObject)
begin
with ManageUsersQ do begin
try
Transaction.Active := true;
if not prepared then prepare;
ExecQuery;
if Transaction.InTransaction then
Transaction.Commit;
ConnectedOk := true;
except
on E:Exception do begin
//only here because user is already logged in
//message from database suffices
if Transaction.InTransaction then
Transaction.RollBack;
ConnectedOk := false;
ShowMessage(E.Message);
Database.Connected := false;
Close;
end;
end;
end;
end;
Now all you need is a flag so you can remove the token
in ManageUsers table on clean exit
delete from ManageUsers where
UName = Database.ConnectParams.UserName;
a better way would be to have a transaction dedicated
to this task and start the transaction OnLogin and
roll it back OnLogOut;
This way you could do something like
Update ManageUsers
set UName = UName
where UName = UName;
if row is already in update your transaction fails
otherwise you keep a lock on while user is connected
If your connection fails Firebird will rollback the
transaction shortly after the connection fails.
In addition you have a table where you can store user
preferences and states between instances
Mick
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