Combining objects and sessions: defining a session handling class - PHP

In order to restructure the example I showed you in the previous section, I’ll simply define a session handling class, in such a way that all the tasks for registering, retrieving and deregistering objects will be handled from inside this class. Here is the signature of the “SessionHandler” class:

class SessionHandler{
    function SessionHandler(){
        session_start();
    }
    // register object as session data
    function registerObject($obj,$objName='defaultObject'){
        if(!is_object($obj)){
            trigger_error($obj.' must be an
object!',E_USER_ERROR);
        }
        if($objName==''){
            trigger_error('Invalid object name.',E_USER_ERROR);
        }
        $_SESSION[$objName]=$obj;
    }
    // deregister object from session data
    function unregisterObject($objName='defaultObject'){
        if(!$_SESSION[$objName]){
            trigger_error('Invalid object name.',E_USER_ERROR);
        }
        unset($_SESSION[$objName]);
    }
    // retrieve session object
    function getObject($objName='defaultObject'){
        if(!$_SESSION[$objName]){
            trigger_error('Invalid object name.',E_USER_ERROR);
        }
        return $_SESSION[$objName];
    }
}

As you can see, the session handling class listed above exposes a few simple methods, handy for registering objects in session variables, as well as for fetching and deregistering them. Based on the functionality provided by this brand new class, the example shown in the previous section can be rewritten as follows:

class DataSaver{
    var $data;
    var $dataFile;
    function DataSaver($data,$dataFile='defaultDir/data.txt'){
        if(!is_string($data)){
            trigger_error('Invalid data type',E_USER_ERROR);
        }
        $this->data=$data;
        $this->dataFile=$dataFile;
    }
    // save data to file
    function save(){
        if(!$fp=fopen($this->dataFile,'w')){
            trigger_error('Error opening data
file',E_USER_ERROR);
        }
        fwrite($fp,$this->data);
        fclose($fp);
    }
    // fetch data from file
    function fetch(){
        if(!$contents=file_get_contents($this->dataFile)){
            trigger_error('Error opening data file',E_USER_ERROR);
        }
        return $contents;
    }
}

// use 'SessionHandler' class to register and deregister objects
$dataSaver=&new DataSaver('This object will be serialized and
saved as session data.');
// save string to file
$dataSaver->save();
// instantiate 'SessionHandler' object
$sessHand=&new SessionHandler();
// register session object
$sessHand->registerObject($dataSaver,'datasaver');
// deregister object
$sessHand->unregisterObject('datasaver');
// retrieve object after deregistering it (triggers a fatal
error)
$sessHand->getObject('datasaver');

In this example, I registered a “$dataSaver” object on a session variable by using the “registerObject()” method that belongs to the “SessionHandler” class. Similarly, the referenced object can be retrieved or deregistered in turn, as shown at the end of the script.

If you’re planning to use your registered objects across different pages during a particular session (as is usually done), again you must include, within all the files, the definition of all the classes that correspond to the objects that will be used.

With reference to the previous example, say you want to restore and use a “DataSaver” object in a different page. This document should be coded like this:

// define sample 'DataSaver' class
class DataSaver{
    var $data;
    var $dataFile;
    function DataSaver($data,$dataFile='defaultDir/data.txt'){
        if(!is_string($data)){
            trigger_error('Invalid data type',E_USER_ERROR);
        }
        $this->data=$data;
        $this->dataFile=$dataFile;
    }
    // save data to file
    function save(){
        if(!$fp=fopen($this->dataFile,'w')){
            trigger_error('Error opening data
file',E_USER_ERROR);
        }
        fwrite($fp,$this->data);
        fclose($fp);
    }
    // fetch data from file
    function fetch(){
        if(!$contents=file_get_contents($this->dataFile)){
            trigger_error('Error opening data
file',E_USER_ERROR);
        }
        return $contents;
    }
}
// define 'SessionHandler' class
class SessionHandler{
    function SessionHandler(){
        session_start();
    }
    // register objects as session data
    function registerObject($obj,$objName='defaultObject'){
        if(!is_object($obj)){
            trigger_error($obj.' must be an
object!',E_USER_ERROR);
        }
        if($objName==''){
            trigger_error('Invalid object name.',E_USER_ERROR);
        }
        $_SESSION[$objName]=$obj;
    }
    // deregister object from session data
    function unregisterObject($objName='defaultObject'){
        if(!$_SESSION[$objName]){
            trigger_error('Invalid object name.',E_USER_ERROR);
        }
        unset($_SESSION[$objName]);
    }
    // retrieve session object
    function getObject($objName='defaultObject'){
        if(!$_SESSION[$objName]){
            trigger_error('Invalid object name.',E_USER_ERROR);
        }
        return $_SESSION[$objName];
    }
}
// instantiate 'SessionHandler' object
$sessHand=&new SessionHandler();
// retrieve registered session object
$dataSaver=$sessHand->getObject('datasaver');
// call 'fetch()' method
echo $dataSaver->fetch();

In this specific example, I explicitly included the definition of all the classes that will be used at a later time, but obviously this should be done by using a “require_once()” statement, in order to simplify the script’s source code. Also, notice how the “$dataSaver” object is properly retrieved via the “getObject()” method that belongs to the “SessionHandler” class. Simple and instructive, right?

At this stage, I think you’ve already grasped the basics of working with objects and sessions, which is an important part of object serialization, since this process is performed internally by the PHP interpreter. From this point onward, you can develop full-featured applications that will smartly combine your objects and sessions.

Finally, the conclusion of this article will rest on setting up a practical example that will demonstrate how to store serialized objects in MySQL tables, instead of using conventional BLOBs.

The last section of the article explains how to achieve this, therefore click on the link below to learn more on this topic.