How to keep data in Joomla module helper class

Question

I've created a module that connects to the database and retrieves some data using

$data = $db->loadRowList();

inside one of the member functions of the module helper class. Is there a way I can store that $data object as a member variable of the class so I can use it in other member functions of the class? My idea is to use $data in my Ajax functions. I've tried defining it like this :

class MyModuleHelper{
    private $data;

    public static MyDatabaseFunction($params)
    {
      ....
      self::$data = $db->loadRowList();
      ...
      //here self::$data is full
    }

    public static MyAjaxFunction()
    {
       //here self::$data is empty
    }
     .....
}

Answer 1

I think you're a little confused as to the relation between static PHP methods/variables and AJAX calls. When you make an AJAX call to the server it's not going to pull up a previously created version of your MyModuleHelper object (even if methods of that object are static). This is because the AJAX call is in a completely different application scope than when the page was loaded.

Think of it this way: two people load the page that has the module. Each page load resulted in a completely independent PHP application/thread being created/executed with a completely different instance of MyModuleHelper (regardless of whether it has static methods/variables). Each person then clicks the button that makes the AJAX call. How does the server know which AJAX call is tied to which MyModuleHelper instance? It doesn't. In fact, those first two PHP applications/executions don't even exist anymore (they completed their work and ended when the page finished loading). The server would create a new PHP application execution and for each AJAX call (with new instances of MyModuleHelper).

That's why your $data is always empty when you make the AJAX call. Static methods/variables are only useful when the same PHP application is using a class and you want to share data (via a static class variable) or use static methods.

The only way to do what you're intending is to make sure $data is populated in any of your function calls that you're calling via AJAX (no need to use static methods or variables):

class MyModuleHelper
{

  var $data = null;

  public populateData()
  {
     // no need to re-populate if we re-call this method for whatever reason
     if(is_object($this->data)) return;

     ...

     $this->data = $db->loadRowList();
  }


  public MyAjaxFunction()
  {
     $this->populateData();

     var_dump($this->data);

     // do stuff
  }


  public MyOtherAjaxFunction()
  {
     $this->populateData();

     var_dump($this->data);

     // do other stuff
  }

}

Hope this helps.

Answer 2

I don't know a lot about static methods as I never work with them, however (and don't quote me on this), it may be because you cannot access non-static properties in a static function.

So you'll either need to define you class property like this:

class MyModuleHelper
{
    static $data;
    ...
}

or move away from static methods, like so:

class MyModuleHelper
{
    private $data;

    public function MyDatabaseFunction($params)
    {
        $this->data = $db->loadRowList();
    }

    public function MyAjaxFunction()
    {
        var_dump($this->data);
    }
}

Hope this helps

Answer 3

I have been writing a lot of ajax modules for work, so I can relate to what you are trying to accomplish with your static methods.

I think you may have a misunderstanding about how/when these static methods are being called.

Via the Joomla handling of ajax processes, the function that looks like:

public static function ModuleNameAjax() {

will be immediately called by default (this is a feature). It doesn't matter what order you write the static methods inside of class modModuleNameHelper { }. The ModuelNameAjax() function WILL BE called, and all other static or non-static functions will remain dormant/un-called until you explicitly call upon them.

If you wish to have immediate access to AND cache the data that is generated from the function MyDatabaseFunction($params), then you will need to call it from inside ModuleNameAjax().

class MyModuleHelper {
    private $data;

    public static MyDatabaseFunction($params) {
        ...
        self::$data = $db->loadRowList();
        ...
        //here self::$data is full
    }

    public static MyAjaxFunction() {
        //here self::$data is empty
        self::MyDatabaseFunction($params); // I'll assume you have access to $params
        //here self::$data should be full and can forever be called by any function
        // from within the class until php terminates the script.
    }
}