Real Time Programing

Posted on 2001-06-21
Last Modified: 2010-05-02

How can I make recoredset that allways connected to DB and changing according to updates in the database.

I meen if I change the data in the table on the SQL server from other computer the recordset will update automatically.

Kind of "Online RecoredSet".

Question by:computech1

Expert Comment

ID: 6213568
you could just call 'requery' each time you access it...

Expert Comment

ID: 6213747
How about using a timer with nutwiss' requery behind it?
LVL 70

Expert Comment

by:Éric Moreau
ID: 6214020
What is your database engine?
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LVL 51

Expert Comment

by:Ryan Chong
ID: 6214425

Expert Comment

ID: 6215053
This is well beyond what current HTML/ASP architecture is supposed to do. But it is possible with a combination of several architectures:

You'll need to do something like:
Create a java applet which uses the Netscape extensions to allow it to talk back to the controlling page (don't forget the MAYSCRIPT)
The java app will open a socket to the web server and wait for messages. When it receives a message it will call a javascript on the webpage to update the relevant fields.
On the SQL server, you can build an activeX extension to send a message to the webserver on demand. You then link this in to update triggers on the tables you want to modify.
On the web server you create an application which can accept requests from the client web pages java apps, and process messages sent from the SQL server, sending the messages out to the client java apps.

Not exactly a simple or elegant approach, but it's more or less the only feasible way you can do this with the current internet architecture.

Anybody know if SOAP can marshall events? This would help things out a lot (in simple terms SOAP is just the java socket app thingy mentioned above, using an XML message)

Author Comment

ID: 6217916

I wanna use only VB6 base on Access/SQL DB.
Don't what to mix with other architectures.

What whould happend if both users update the same record in same moment ? ?

Author Comment

ID: 6217926
What Whould happend if both users update the same record ?

Accepted Solution

andyclap earned 100 total points
ID: 6218182
Ooops, I misinterpreted your question (I was browsing the ASP topic at the time and presumed you meant a web architecture).

A periodic refresh as mentioned by others above will keep your data in synch, but dynamic syncronisation across applications is not a feature of any of the database technologies available from VB. You could create your own architecture (such as using sockets as above) to do this, but it's not easy. It's pretty impressive for clients if you do manage to do this - they love "live" data. I use this in my current project but the architecture behind it is huge and very complicated.

>What whould happend if both users update the same record in same moment ? ?
It's up to you - there are two commonly used levels of protection:

Optimistic - no specific locking of records, so if two people update, both updates are applied, and the last one 'wins'. This is commonly used in conjunction with a timestamp value which is checked on the update against the original value to ensure the user is updating the version of the record that they are looking at, usually with a "Data has changed, please refresh" message if it fails.

Pessimistic - When data is retreived, the data is locked for update and cannot be displayed for update by anyone else until the data is released again. Can cause massive contention if being used in interractive screens, usually only used in single internal processing chunks. Not really viable for a web based solution at all as there is no persistant connection so you get optimistic locking anyway.


Expert Comment

ID: 6783324

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