（PrestaShop）从核心类调用静态方法的正确方法

One of the core files classes/stock/StockAvailable.php contains:

class StockAvailableCore extends ObjectModel
{
   public static function getQuantityAvailableByProduct($id_product = null, $id_product_attribute = null, $id_shop = null)
     {
       ...
     }
  ...
}

I want to call this getQuantityAvailableByProduct() method from my module.

So I tried to include this class (and it's father class and father's interface), extend it and call method like this:

require_once('../../src/Core/Foundation/Database/EntityInterface.php');
require_once('../../classes/ObjectModel.php');
require_once('../../classes/stock/StockAvailable.php');

$MyClass = new StockAvailableCore();

$MyClass->getStockAvailableIdByProductId($id);

And the error that I'm getting:

PHP Fatal error:  Uncaught Error: Class 'ObjectModel' not found in /home/mantas/Server/honey/classes/stock/StockAvailable.php:34

What am i missing? And is this the correct way to extend a class and call method?

ObjectModel.php file

<?php

    class ObjectModel{

        //For example I created non-static function in ObjectModel class
        public function getStockAvailableIdByProductId($id){
            return "test";
        }

        //For example I created static function in ObjectModel class
        public static function getStockAvailableIdByProductIdStatic($id){
            return "teststatic";
        }

    }
   ?>

StockAvailable.php file.

<?php
//Extends used to inherit the parent class property
    class StockAvailableCore extends ObjectModel
    {
       public static function getQuantityAvailableByProduct($id_product = null, $id_product_attribute = null, $id_shop = null)
         {

         }

    }


    ?>

run.php file

<?php

require_once('ObjectModel.php');
require_once('StockAvailable.php');

$MyClass = new StockAvailableCore();

// Access the ObjectModel function

//to access the  Non-static method need to create the object.
echo $MyClass->getStockAvailableIdByProductId($id);

//Static method access by class reference (::)
echo StockAvailableCore::getStockAvailableIdByProductIdStatic($id);
?>

You can call it just in this way StockAvailable::getQuantityAvailableByProduct($id_product, $id_product_attribute) . And if you make your module according to Documentation you don't even need to include any files at the beginning of your code