php variable scope with AJAX calls

Question

What scope to php variables have with regards to AJAX calls? So for example, a file main.php creates an instance of a class Test:

<html>
  <head>
    <?php
      require_once 'test.php';
      $test = new Test('some parameter');
    ?>
  </head>
  <body></body>

</html>

Later on there is a jQuery post event triggered by some event:

$(document).ready(function() {

  $.post(   
    "class/start.php",   
    function(data) {
      // some functioning.              
    }, "json");

});

Then in start.php I need access to the class I defined in main.php. E.g.:

<?php
  echo json_encode($test->SomeFunction());
?>

From testing this I'm fairly sure this isn't possible. I assume the scope of $test dies when main.php comes from the server. So what do I need to do to access the instance of that class? Do I need to add $test as a session variable or is there some other better way?

Jonathan M · Accepted Answer · 2011-08-17 19:35:29Z

2

You could session_start() and put $test in $_SESSION['whatever'].

You'll need to session_start() as the first thing in the php activity for both HTTP requests. In the second HTTP request, just json_decode() the object and then add it to $_SESSION['whatever'].

In case you're not familiar with sessions, they basically give you the ability to retain state, storing state data in $_SESSION[]. See here: http://www.php.net/manual/en/function.session-start.php

edited Aug 17, 2011 at 19:35

answered Aug 17, 2011 at 19:28

Jonathan M

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1 Comment

Ciarán Tobin Over a year ago

OK thank you for your response. I thought that I may have to do this, but wasn't sure if it was completely necessary.

Naftali · Accepted Answer · 2011-08-17 19:27:33Z

2

You need to recreate $test on the json page:

<?php
      require_once 'test.php';
      $test = new Test('some parameter');
      echo json_encode($test->SomeFunction());
?>

answered Aug 17, 2011 at 19:27

Naftali

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2 Comments

Ciarán Tobin Over a year ago

But I need access to the same instance of Test. Looks like I have to add it as a session variable?

Naftali Over a year ago

@MadScone -- you can try, but you might have to serialize it 1st.

red · Accepted Answer · 2011-08-17 19:28:34Z

1

These are two separate calls to PHP: the first one is your loading page (main.php) and the second is in the ajax call (start.php). Therefore, you need to require/include test.php again in your start.php.

answered Aug 17, 2011 at 19:28

red

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Comments

gen_Eric · Accepted Answer · 2011-08-17 19:33:57Z

1

add it to session on first request

$_SESSION['test'] = serialize($test);

and in start.php

$test = isset($_SESSION['test']) ? unserialize($_SESSION['test']) : 'no test';

and print it to repsponse

edited Aug 17, 2011 at 19:33

gen_Eric

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answered Aug 17, 2011 at 19:28

Senad Meškin

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Comments

Jeff Lambert · Accepted Answer · 2011-08-17 19:28:44Z

0

main.php is requested from the server. All server side code is evaluated and executed, and a response is sent. At that point, the script is complete.

Some time after that, an AJAX request hits the server. This is a completely separate request, and any data that you need to recreate the class 'test' needs to be sent along with the request in GET or set in SESSION.

answered Aug 17, 2011 at 19:28

Jeff Lambert

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Comments

GSto · Accepted Answer · 2011-08-17 19:29:00Z

0

when you make an ajax request, you are starting a new PHP request, so none of the variable in one will be availble in the other unless passed explicity through JSON. you could store it in session, or you could pass your 'some parameter' string to the requested script and construct the Test object there.

answered Aug 17, 2011 at 19:29

GSto

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Comments

Jonathan Cremin · Accepted Answer · 2011-08-17 19:30:44Z

0

HTTP is a stateless protocol, everything starts from scratch between requests.

You don't typically put objects in sessions as it can lead to unexpected behaviour. You should instead reinstantiate Test in start.php.

If Test needs to retain state (the values of some variables), you should break that state out and store it in a session on its own.

answered Aug 17, 2011 at 19:30

Jonathan Cremin

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gen_Eric · Accepted Answer · 2011-08-17 19:30:52Z

0

In main.php, $test is a global variable, which will exist until PHP is done executing. When the browser shows the page, that means PHP is finished executing.

When you make an AJAX call to start.php, PHP starts again, and unless you include main.php it has no idea about $test.

You need to re-declare $test on start.php, or declare it in another file, and include it in both main.php and start.php.

answered Aug 17, 2011 at 19:30

gen_Eric

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