Correct way to extend Prestashop 1.7 - prestashop

Question

In PS 1.7 documentation, we can read multiple time that the PS override system is not recommended, an it's not allowed to publish module in the PS marketplace.
We have to only use hooks, and extend existing class, and I understood why.
But how to use the extended class instead of the core one in our custom theme ?
Let use a example :
I want to add a custom field for categories.
In a module I extend the CategoryCore class :
class Category extend CategoryCore{
private $bottom_description
...
}
Then to add the field in the category's admin page I can use some hook like displayBackOfficeCategory and actionBeforeAddCategory.
But I'm not sure for the front : the new variable have to be accessible in some theme templates files.
In my custom theme, in the category.tpl template, $category->bottom_description is undefined.
Fix this issue by overriding the CategoryController is easy,but how to do this only with hook ?
The only way I found is to use the actionFrontControllerSetMedia hook, like this :
function HookActionFrontControllerSetMedia(){
// get my custom Category object base on url
this->context->smarty->assign(["category_bottom_description"=>$category->buttom_description]);
}
This look tricky, and my new field is still not accessible in other context.
So what is the proper way to get this property available in my custom them ?
Ideally, the new property should be available every time we found a category object, like this : $category->bottom_description.

Answer 1

Do not forget to define a new field at category class because at the front you have not a class instance but an array which is converted within ObjectPresenter class. So follow this way. Extend your Category class and add all necessary definitions
class Category extends CategoryCore
{
public $bottom_description;
public function __construct($idCategory = null, $idLang = null, $idShop = null)
{
Category::$definition['fields']['bottom_description'] = array('type' => self::TYPE_HTML, 'lang' => true, 'validate' => 'isCleanHtml');
$this->bottom_description = 'bottom_description'; // just to add demo data
parent::__construct($idCategory, $idLang, $idShop);
}
}
and then the field bottom_description will be available in the category.tpl but like an array {$category.bottom_description}. Hope it will help you.