Thread: Auto Update Client Page Without Constant Refresh

Hi.

I have been asked to look into developing an online takeaway/delivery order system. It all seems fairly straightforward except for one part, getting the orders through to the takeaway outlets.

I am aware that I can just set up a computer within the outlet, connect it to the internet and log them into the system on an "auto-refresh" page which will list all the latest orders. However this seems a bit resource heavy.

Is there a way in which I can automatically post data from the server to the client (computer in an outlet, either onto the screen or via a printer). There was a thread a few weeks ago about Facebook using AJAX to do this, anyone know how?


Any help would be brilliant,
Josh.

Yeah I think you're referring to my thread.. How to auto update... - Webmaster Forum

I didn't get much out of that either.. I'd still like to know if anyone has experience in this..

Yeh it was your thread indeed.

It would be great to know how to do it, a lot of the LiveChat systems are using it now so someone must know how! It saves having to waste a load of resources on auto-refreshing the page.

articweb added 1296 Minutes and 45 Seconds later...

Asked on Yahoo! Answers and got the following replies:

Originally Posted by Yahoo! Answers (mipav200...)

Ajax has this thing called xmlhttprequest which can do a http request without reloading the page. That is all you can do.
So: from time to time do a xmlhttprequest, get the new data and post it on the website without reloading it

and...

Originally Posted by Yahoo! Answers (just "JR")

You have three "machines":
- The buyer's machine, the one that places the order and send it to the server.
- The server, who receives the order, and updates the database.
- The Shop monitor, who "looks" at the database.
Remember one thing: a server NEVER send anything to anyone by itself: the server only RESPONDs to a request.

So, the Shop monitor asks the page, receives it, then... do nothing.
The database can be updated 1000 times, the monitor will NOT be informed, UNLESS it makes a request.
To do this (and it is the technique of most chat boards), you set-up a small timer in the Shop monitor page, sending a request every, say, 5 seconds, to the server. (for a chat, every 2-5 sec is ok, for orders, maybe 20, 60 secs? - to be adjusted).
On the request, the server checks if the order list has "changed" (more records or something else). It the order list has not changed, the server sends a reply "nothing new" (sort of), otherwise, it sends a reply to update a part of the screen (AJAX).
You could have a part of the screen as a scrollable box, or an iframe. The server sends the order list from the last first, refreshing the list every x secs. The rest of the screen does not change.

Very scarce on ressources!

Yahoo! Answers: How can I make a page automatically update when a database table is updated?




This coupled with W3 schools tutorials and Google managed to provide me with the knowledge I wanted. Hopefully it's of use to a few other people?

Thanks artic.. let me know if you get everything working the way you want it to please