Question

I hope I worded the title accurately enough but I typically use Java and don’t have much experience in Web Development/PHP/CodeIgniter. I have a difficult time understanding the life cycle of a script as I found out trying to implement a certain feature to a website I am developing (as a means of learning how to). I’ll first describe the feature I tried implementing and then the problem I ran into that made me question my fundamental understanding of how scripts work since I’m used to typical OOP.

Ok so here goes…

I have a webpage that has 2 basic tasks a user can do, create and delete an entry. What I attempted to implement was a way to time a user how long it takes them to complete a certain task. The way I did this was have a homepage where there would be a list of tasks a user to choose from (in this case 2, create and delete). A user would click a task which would link to the ‘true’ homepage where the user then would be expected to complete the task. My script looks like this:

<?php

class Site extends CI_Controller {

var $task1;
var $tasks = array(
                        "task1" => NULL,
                        "date1" => 0,
                        "date2" => 0,
                        "diff" => 0);

function __construct()
{
    parent::__construct();
    include 'timetask.php';
    $this->task1 = new TimeTask("create");      
}   

function index() 
{   
    $this->tasks['task1'] = $this->task1->getTask();
    $this->tasks['diff'] = $this->task1->getTimeDiff();

    if($this->tasks['diff'] == NULL)
    {
            $this->tasks['diff'] = 0;
    }   

    $this->load->view('usability_test', $this->tasks);
}

function origIndex() 
{   
    $this->task1->setDate1(new DateTime());
    $this->tasks['date1'] = $this->task1->getDate1()->getTimestamp();
    $data = array();

    if($q = $this->site_model->get_records())
    {
        $data['records'] = $q;
    }

    $this->load->view('options_view', $data);
}

function create()
{
    $this->task1->setDate2(new DateTime());
    $this->tasks['date2'] = $this->task1->getDate2()->getTimestamp();

    $data = array(
            'author' => $this->input->post('author'),
            'title' => $this->input->post('title'),
            'contents' => $this->input->post('contents')
    );  

    $this->site_model->add_record($data);
    $this->index();

}

I only included create to keep it short. Then I also have the TimeTask class, that actually another StackOverflow so kindly helped me with:

<?php

class TimeTask
{
private $task;

/**
 * @var DateTime
 */
private $date1, $date2;

function __construct($currTask) 
{
    $this->task = $currTask;
}

public function getTimeDiff() 
{
    $hasDiff = $this->date1 && $this->date2;
    if ($hasDiff) {
        return $this->date2->getTimestamp() - $this->date1->getTimestamp();
    } else {
        return NULL;
    }
}

public function __toString() 
{
    return (string) $this->getTimeDiff();
}

/**
 * @return \DateTime
 */
public function getDate1()
{
    return $this->date1;
}

/**
 * @param \DateTime $date1
 */
public function setDate1(DateTime $date1)
{
    $this->date1 = $date1;
}

/**
 * @return \DateTime
 */
public function getDate2()
{
    return $this->date2;
}

/**
 * @param \DateTime $date2
 */
public function setDate2(DateTime $date2)
{
    $this->date2 = $date2;
}

/**
 * @return get current task
 */
 public function getTask()
 {
        return $this->task;
 }

}

?>

I don’t think posting the views is necessary for the question but here is atleast how the links are made.

<?php echo form_open('site/create');?>
...and...
<?php echo anchor("site/delete/$row->id", $row->title); ?>

Now there’s no error in the code but it doesn’t do what I expect of it and the reason I assume why is because that each time a function of the script is called via a new page it is NOT the same instance of the script called previously so any previously created objects are no longer there. This confuses me and leaves me quite unsure of how to implement this gracefully. Some ways I would guess of how to do this is by passing the necessary data through the URL or have data saved in a database and retrieve it later to compare the times. What would be a recommended way to do, not just this, but anything that needs previously created data? Also, am I correct to think that a script is only ‘alive’ for one webpage at a time?
Thanks!

Answer 1

Web development is a bit different to “standard” development – principally because of the nature of HTTP. Each request to the web application has to travel across the network using HTTP, which, as all web developers know, is stateless. What this means is that web servers do not have to remember anything about previous HTTP requests. Usually, webdevs get round this using cookies in one way or another – where a cookie is some bit of data, coded as a text string, which is sent back to the browser so that it can resend it to the application on the next request. Like that, a cookie is a kind of transferable memory.

So, each time you make a request, unless you transfer some data using a cookie (either an HTTP cookie, or what is sometimes called a URL cookie – state data coded in the URL), it looks to the web application like a brand new request, unrelated to any past request. So, for your application to work, you need to use a cookie in some way to remember or recover the start time when you detect that the user has finished a task. You can either (i) use CI’s built-in facilities for remembering data (flashdata, as mentioned above, or userdata from the CI Session class – see http://codeigniter.com/user_guide/libraries/sessions.html), which are built on top of CI cookies), (ii) do this using your own cookie data (not recommended – why use the framework in that case?), or (iii) use hidden form fields – an oldie but sometimes goldie technique that requires the PHP script generating a view to write hidden form fields whose values are the data you want to remember and have sent back to you on the next request.

This kind of problem is something you’ll come across again and again in web development – so get to know the problem and its solutions well!