The PHP documentation says "You can't use references in session variables as there is no feasible way to restore a reference to another variable."
Does this mean I can't have things like:
session_start();
$user = new User;
$user->name = 'blah';
$_SESSION['user'] = $user;
I have tried to store a simple string and a User object in session, the string always persists between pages to pages, or after page refresh. However the User variable is lost in $_SESSION(becomes empty).
any idea?
Edit:
I have confirmed that session_id is the same in all of these pages/subpages,before & after page refresh.
Edit:
Strangely, after I tried serialize and unserialize approach below, the serialized user object(or string) in session still still disappears!
Edit:
finally I figured out what the bug was, looks like somehow $_SESSION['user'] gets overwritten by some mysterious force, if I use any variable other than 'user', then everything's fine. PHP(at least 5.3 which is the version I'm using) does serialize and unserialize automatically when you put object in the $_SESSION.
session_start();
$user = new User();
$user->name = 'blah'
$_SESSION['myuser'] = $user;
You need to use the magic __sleep and __wakeup methods for PHP 5 Objects.
For example in the following code block:
$obj = new Object();
$_SESSION['obj'] = serialize($obj);
$obj = unserialize($_SESSION['obj']);
__sleep is called by serialize(). A sleep method will return an array of the values from the object that you want to persist.
__wakeup is called by unserialize(). A wakeup method should take the unserialized values and initialize them in them in the object.
Your code example isn't using references as the documentation was referring to. This is what php means by references:
$var =& $GLOBALS["var"];
As to putting objects into the session, PHP can store objects in $_SESSION. See http://example.preinheimer.com/sessobj.php.
What you are seeing is a bug in the order of calls to __sleep and __destruct (__destruct is being called before __sleep) and the session module fails to serialize the object at shutdown. This bug was opened on Sep 1, 2009.
For safe serialization and unserialization encode and decode with base64_encode() and base64_decode() respectively. Below I pass a serialized Object to a session and unserialize it on the other page to regain the variable to an object state.
Page 1
<?php
require $_SERVER['DOCUMENT_ROOT'] .'/classes/RegistrationClass.php';
$registrationData= new RegistrationClass();
$registrationData->setUserRegData();
$reg_serlizer = base64_encode(serialize($registrationData)); //serilize the object to create a string representation
$_SESSION['regSession'] = $reg_serlizer;
?>
Page 2
<?php
session_start();
require $_SERVER['DOCUMENT_ROOT'] .'/classes/RegistrationClass.php';
$reg_unserilizeObj =
unserialize((base64_decode($_SESSION['regSession'])));
$reg_unserilizeObj->firstName;
?>
This article describes issues that may be faced by not doing so.
issuses with php serialization/unserialization
You were right saying you can not store references in sessions variables
assigning an object in PHP 5 and above is doing just that assigning the reference not the obj
That its why you would need to serialize the object (implementing also __sleep in the Class) and assigning the string to a session variable
and deserializing it later (implementing also __wake in the Class) from the session variable later on.
That's the expected behavior. Storing a reference to an object would only work if the memory location for the object didn't change. In a stateless protocol like HTTP, application state is not persisted between requests. The next request may be handled on another thread, process, or another server.
Given the inherent stateless nature of a web application, holding a pointer to a memory location is useless. Therefore the object's state must be broken down into a storage format, saved or transmitted, and then reconstituted when needed. This process is known as Serialization.
You can choose to serialize the entire object into session (which maybe dangerous depending on the depth of your object graph, since your object may hold references to other objects and those would need to be serialized as well), or if the object can be reconstituted by querying the database on the next request you may just stash an ID in the session.
[EDIT]
JPot pointed out that objects are automatically serialized to $_SESSION, so explicit serialization isn't necessary. I'll leave the answer for posterity, but obviously it doesn't help your problem.
Related
I have a serialized object in the session.
When I want to change just one property of this object, is this really the only way to go:
$foo = $session->get('foo');
$foo->setBar('Hello');
$session->set('foo', $foo);
Isn't there a way to modify the property directly in the session, without having go fetch the entire object from the session?
Something like $session->set('foo.bar','Hello');
EDIT: I have read http://symfony.com/doc/current/components/http_foundation/sessions.html#attributes but (as I understand it) this applies only to arrays, not objects. In any case, $session->set('foo/bar', 'hello'); doesn't work: It creates a new entry in session (sibling to foo), named foo/bar.
Like I said in a comment you can use this solution:
$session->get('foo')->setBar('Hello');
I hope this helps!
In my PHP code, I create a 'session' object that stores user type, auth etc. (although no password in any form). Then I serialize this object into the $_SESSION var:
$_SESSION['sess_data'] = serialize($session);
when I need to authenticate the user, I do this:
$session = unserialize($_SESSION['sess_data']);
It looks very unsafe to me though. How can I improve it? Would some method as get_class() suffice? Thanks
just a small question regarding the php session handler,
let's say i want to store the session in a database because i have multiple servers that should have access to the session, i would write my own sessionhandler using the interface as described in http://php.net/manual/en/class.sessionhandler.php,
but how can i use it?
if i do
session_set_save_handler(....);
session_start();
$_SESSION['key'] = 'value';
will it save the data using my handler?
The class that you define and set in set_save_handler() should have all the functions required in the lifetime of a session to be defined. These include read(), write(), destroy() among others.
Once that is defined correctly you can still manipulate sessions the normal way you do, but in the background, the functions you define will get executed based on which session event you are performing.
For e.g. $_SESSION['key'] = 'value' will perform the write() function (in which you might have coded a database save routine)
You can read more about it at: http://us3.php.net/manual/en/function.session-set-save-handler.php
With the use of static variables and the singleton pattern, I thought that it would be easy enough to create a simple shopping cart that remembered what items where in the cart when another page was loaded.
I am having a problem of the shopping cart not remembering what was already in it when the page is refreshed.
Is there a problem with my code below or should I just use globals or a mysql database.
What is the best way to go about storing state..
<?php
//create a singleton class
class shoppingCart {
private static $_shoppingCartItems = array();
private static $_instance = null;
private function __construct(){
}
public static function getInstance(){
if(self::$_instance == null)
self::$_instance = new shoppingCart();
return self::$_instance;
}
public function add(ShoppingItem $item){
$this->_shoppingCartItems[] = $item;
}
public function cartCount(){
return count($this->_shoppingCartItems);
}
}
?>
Implementation
$item = new shoppingItem();
$shoppingCart = shoppingCart::getInstance();
$shoppingCart->add($item);
$shoppingCart->add($item);
//should increment by 2 on each page load but it doesn't
echo $shoppingCart->cartCount();
Static class members (or any other variables for that matter) are not preserved across different requests. Never.
Sessions to the rescue
The only exception to this is $_SESSION; which is a special mechanism to allow for just that.
Star the session with session_start() at the top of your script.
You can now use $_SESSION like a regular array to store and retrieve information. A session belongs to a single user, it is not a means of sharing data across all your users.
Have a look here for an introduction.
Silence
You must not output anything before session_start() is called. That is to say, <?php must be the exact first thing in a PHP script that wishes to use sessions. Further, there must be no echo statements or any other output generating functions between <?php and session_start().
Output Buffering
If you really must generate output before starting the session, you can use output buffering.
Notes
$_SESSION is forgetful. After a certain time of inactivity on the user's side, the data will be deleted.
If you get the following error message, you violated the above guidelines. Another possibility is that your script has a BOM (Unicode byte order mark). If so, remove it.
Warning: session_start(): Cannot send session cookie - headers already
sent by (output started at
The reason this happens is due to the way PHP handles output: It tries to get the output as fast as possible to the user. However, the HTTP protocol transmits certain control data (cookies, which session belongs to you etc), called "headers" before all the output ("body") of the response. As soon as you output anything, the headers need to get sent - unless you use output buffering that is.
I think I can see your thought pattern there but what you're trying to do is wrong in many ways.
1. Singleton is NOT a pattern, it's an antipattern
The Singleton is an anti-pattern and should be avoided at all costs. See this great answer by Gordon for the why.
2. HTTP is a stateless protocol.
Nothing you do in PHP alone will help you to preserve state across two requests. Your $shoppingCart is created from the scratch for each request, in fact, your whole application is. You should NOT try to persist data in objects instead you should recreate state after every request, by fetching the respective data from somewhere else. In your example probably from some sort of database nosql or sql.
3. Sessions
You can persist user specific data in the superglobal $_SESSION, but in most cases I advice against it. Your user session should hold authentication and user data but you should avoid storing all kinds data relevant for your business logic in there.
PHP is not an application server. It will not automatically persist your "application" state between requests. You have to do that yourself via $_SESSION, cookies, and/or your own private methods.
Unless you take steps to preserve data, the state of the application is wiped when the HTTP request that invoked the script(s) is ended.
I have instantiated a class in my index.php file. But then I use jQuery Ajax to call some PHP files, but they can't use my object that I created in the index.php file.
How can I make it work? Because I don´t want to create new objects, because the one I created holds all the property values I want to use.
Use the session to save the object for the next page load.
// Create a new object
$object = new stdClass();
$object->value = 'something';
$object->other_value = 'something else';
// Start the session
session_start();
// Save the object in the user's session
$_SESSION['object'] = $object;
Then in the next page that loads from AJAX
// Start the session saved from last time
session_start();
// Get the object out
$object = $_SESSION['object'];
// Prints "something"
print $object->value;
By using the PHP sessions you can save data across many pages for a certain user. For example, maybe each user has a shopping cart object that contains a list of items they want to buy. Since you are storing that data in THAT USERS session only - each user can have their own shopping cart object that is saved on each page!
Another option if you dont want to use sessions is to serialize your object and send it through a $_POST value in your AJAX call. Not the most elegant way to do it, but a good alternative if you don't want to use sessions.
See Object Serialization in the documentation for more informations.
mm, you should store in session, $_SESSION["someobj"] = $myobj;, and ensure that when you call the Ajax PHP file this includes the class necessary files which defines the class of $myobj and any contained object in it.
Could you be more specific? I can try.
This is how I create an object then assign it to a session variable:
include(whateverfilethathastheclassorincludeit.php)
$theObject = new TheObjectClass();
//do something with the object or not
$_SESSION['myobject'] = $theObject;
This is how I access the object's members in my Ajax call PHP file:
include(whateverfilethathastheclassorincludeit.php)
$theObject = $_SESSION['myobject'];
//do something with the object
If you don't want to move your object that is in your index.php, have your ajax make a request to index.php but add some extra parameters (post/get) that let your index.php know to process it as an ajax request and not return your normal web page html output.
You have not provided code, but what I guess is that you need to make your instantiated object global for other scripts to see it, example:
$myobject = new myobject();
Now I want to use this object elsewhere, probably under some function or class, or any place where it is not getting recognized, so I will make this global with the global keyword and it will be available there as well:
global $myobject;
Once you have the object, you can put it into the session and then utilize it in the Ajax script file.
As others have suggested, $_SESSION is the standard way to do it, in fact, that was one of the reasons, that sessions where invented to solve. Other options, i.e. serializing the object rely on the client side to hold the object and then return it untampered. Depending on the data in the object, it is not a good solution, as a) the object may include information that should not be available on the client side for security reasons and b) you will have to verify the object after receiving it.
That said, and if you still want to use the object on the client side, then JSON is an option for serializing object data, see JSON functions in PHP.
Based on most of the answers here, referring to storing the object in $_SESSION, is it more efficient to store only the individual properties that need to be accessed in AJAX as opposed to the whole object, or does it not matter?
E.g.
$_SESSION['object'] = $object;
vs
$_SESSION['property1'] = $object->property1;
$_SESSION['property2'] = $object->property2;
I know the OP is asking about accessing the entire object, but I guess my question pertains to if it's just a matter of only accessing certain properties of an object, and not needing to access methods of a class to alter the object once it's in AJAX.