[SOLVED] ASP - AJAX (Retrieve Database Value Without Refreshing The Page)

[Monie]

I've just know that this was a great way to display our data inside the database to be display in our page without keep refreshing the page for new incoming data!

Does anyone know how this thing is done? I mean, how do the XML code retrieve the data from my database and display it to my page?

Thanks..

[spinal007]

You use PHP/ASp to call the database and generate the XML.

This allows you to...
1. save it on the server and load the file with PHP/ASP without needing to make a database call
2. send the XML to the client and manipulate it with Javascript
...amongst other things

[alexgeek]

not really sure how XML parsing works in ASP. But in .NET and PHP it's extremely easy.

[spinal007]

It's not naturally as easy to do it in ASP, but there are open source classes out there that make it easy... But usually, the best use of XML is on the client.

If you cache XML on the server, you reduce the load on the database server, not on the web-server. But if you use a client-side interface to manipulate the XML, you reduce the load on the web-server AND the database server.

And the key thing is, database systems (such as MySQL and MSSQL) are built to deal with high-stress applications. The slowest part of a website is usually the web-server itself - not the database.

Hope that helps anyone...

[alexgeek]

I don't like to rely on the client side to manipulate XML personally.
Could you give me an example of when you would do this?

[spinal007]

erm... you got me there. I support the theory, but I haven't actually used this technique in any of my projects. You can throw me in the closet and tell me to "practice what you preach"...

But I would use this technique in any Ajax application that uses a permanent data source within a page - for local searching instead of calling the server over and over for a new 'filtered' copy.

AH! Yes I do use this, for several things actually, one of which is an email autocomplete input (an address book lookup)

[alexgeek]

Ahh fair play. Good use.

[Monie]

This is a bit confusing!
What about AJAX/XML? Do they related in terms of displaying new data (from database) without refreshing the page?

[spinal007]

ok monie, I'll explain - and for that I will assume you understand these terms:
- client: the machine viewing the webpage, the visitor's computer
- server: the machine where your website is hosted
- database server: the machine where the database is hosted
(websites and databases are not usually hosted together)

Let's consider an address book lookup in Javascript, as I mentioned above.
you need:
a) Data - a "list" of names and email addresses
b) Functionality - the ability to search

Let's assume the 'data' is on your database server and the client will access it via your website.
1. Client requests page from web-server
2. Web-server runs script connects to database and retrieves data
3. Web-server processes data and sends a response
4. The response is processed by the client's browser (they see it some how)

In the most common scenario, the web-server will ask for the database to give it some data. The database server will take care of searching. The web-server will only deal with 'presenting the data'.

When the user searches again, you will have to go through all those stages again. This is a classic web-application - no caching involved - simple, raw, get the job done. But this isn't good enough if you care about performance or if you are building a large-scale application.

So that's where XML comes in (there are other formats but let's just assume XML is the way to do it)

If you save the data from the database on the web-server, you allow yourself to skip step 2. You don't have to call the database server again. But then, there will be more processing for the web-server to do. It will have to get the file from somewhere and perform any search functionality required.

If you use the web-server to send ALL the data to the client - let's say, in XML format - without any filters (not searched) then you can skip step 1, 2 and 3 from then on.
What happens now is that you leave the processing (searching through the data) to the client AND you cut off all the traffic between the client, your web server AND your database server.

Go to run - hope you understand it now!

(perhaps I could turn this into an article...)

[alexgeek]

I understand the concept but I don't see how you would store the XML on the client's machine.

[spinal007]

you don't store it as such - like saving a file, etc...

you just request it via javascript (Ajax), then it's stored in memory, until you leave or refresh the page.

[alexgeek]

I understand now. Thanks.
Would be a great article actually (in fact a tutorial would be preferable).

[spinal007]

I've never been good at writing tutorials, but I'll have a go at writing an article...

[Monie]

I am new to this ASP-XML-AJAX things...

I've been googling around to learn the concept of "retrieving data from database without refreshing the page" things... and sadly I must say I have ended up with nothing, practically.
I understand the concept that you've explained to us, but practically.. I have no idea!

P/S: I have found some example in ASP/XML/AJAX for the ASP Chat, Search and Display, but it's not what I wanted to do!
What I want to learn is, when there is a new input in my database, it will trigger something to you, our PM Alert Message Popup Box is the close example that I can give you

[spinal007]

Forget about this conversation - it's too abstract and too advanced for you. I'm not sayin you will never get this, but you can only appreciate what we're talking about if you already know how to use databases (and I thought you did).

Start off by learning how to use a simple database (I'd recommend MS Access if you have MS Office or MySQL if you have one).

1. First learn about databases: how to make a table, etc
2. Then learn to read from/write to databases - there's tons of tutorials out there (1, 2, 3, 4, ...)