Override Prestashop 1.6.1.4 - php

Question

I am doing a module in Prestashop and I need override the method update in the class CartCore. I have created a class inside the folder override (I have tried in modules/name_of_module/override also) Cart extends CartCore (the file is Cart.php), and I have the next code.
public function update($null_values = false, $hook = true)
{
if (isset(self::$_nbProducts[$this->id])) {
unset(self::$_nbProducts[$this->id]);
}
if (isset(self::$_totalWeight[$this->id])) {
unset(self::$_totalWeight[$this->id]);
}
$this->_products = null;
$return = parent::update($null_values);
if($hook) Hook::exec('actionCartSave');
return $return;
}
I have deleted the file cache/class_index.php and I have activated the overrides in the back-office Performance but it does not work. Only works if I change the original Cart class, but I don´t want do this.
Thanks!

Answer 1

When you create a new Override in a module Prestashop isn't aware of this new file. Deleting the /cache/class_index.php will only force Prestashop to look for new files in the root /overrides/ folder but not in your module /modules/your_module/overrides/ folder.
Your file needs to be placed under the root /overrides/ folder. This process is done automatically when you install your module. Every override files in your module is placed under the root /overrides/ folder. If you create a new override while your module is already installed, Prestashop will not move it for you.
You then have two possibilities. Uninstall and install your module. Or copying this file into the root /overrides/ folder and deleting the /cache/class_index.php file.
Also take into account Niclas Larsson advise to put this file under /overrides/classes/Cart.php.

Answer 2

Overriding default behaviors
Overriding a class
In order to override the Product class, your file needs to be called Product.php and must feature a Product class that then extends ProductCore class.
The file can be placed in either of these locations:
/override/classes/Product.php
/modules/my_module/override/classes/Product.php
Override files a separated in folders based on their types (classes, controllers, modules, ..)
So i think you are doing things right, but you need to add the folder 'classes' in override, and move your file into it.