Since version of PrestaShop, there is a new feature that allows developers to override a module’s instance classes (ie. its main module files, see the PR by @axometeam).

Since PrestaShop uses lots of modules for both core and custom features, module overrides are a welcome addition to an already great override system in PrestaShop. Let’s take a look on how to use it.

Override a module’s instance class by extending it

To override a module’s instance class, you have to extend it, giving the extended class the same name and adding Override suffix:

This file should be put in /override/modules/blockuserinfo/blockuserinfo.php.

When you manually add an override, do not forget to clean the class reference cache by deleting cache/class_index.php. The next time PrestaShop loads, it will regenerate class_index.php and your module override will be active!

You may even make a module that has overrides for other modules! For example, /modules/mymodule/override/modules/blockuserinfo/blockuserinfo.php will be copied to /override/modules/blockuserinfo/blockuserinfo.php during the installation of the mymodule module. However, this is not recommended, since the exact usage of a module to be overridden is unknown and may be different in a particular shop.

Troubles overriding some modules

Some modules (mainly core modules) have methods that can’t be extended (at the moment).

For example:

As you can see, this class has a variety of properties and methods. Some methods are public, some are protected and others are private.

Sometimes you may need to extend a method that is currently set to be private. Unfortunately, it is not possible to extend private variables or methods in PHP (and most other class-based programming languages).

This is a design issue. Core modules were written long before the introduction of module overrides. Difference is that private scope “locks down” class features, while protected scope is less strict and allows overrides by a child class.

If you come across a core module method that is private, the best thing to do is change it to protected and to make a pull request on GitHub for that module. Everyone will benefit!

How to make cleaner method overrides

Overrides are great, but do they keep up with the updates? We are talking about a situation where the whole function is copied to an override and one minor modification is made:

We added the line 'company_name' => ($this->context->customer->logged ? $this->context->customer->company : false),, which adds a company_name Smarty variable that we want to use in our template.

The problem is that we essentially “snapshotted” the method code that we took from the module. The code of this method may and will change in the future version. What if wanted to have the updated code but also add our one little modification?

When the code structure and logic allows it, you should always aim to execute the whole unmodified parent method and then (before or after) add that one little modification. The way you can do this is by using parent keyword, which calls the method from the parent class:

In the example above, we add our Smarty variable, and then return the parent method, which will call the unmodified and possibly updated hookDisplayTop method. There is no need to copy the whole method.

P.S. There is one small issue in the example, which you may have noticed. In the parent method, there is a statement, if (!$this->active), which should’ve been taken into consideration when making the override. We could put it in our overridden method, or for the purpose of this example, we can imagine that it’s not there :)

Module overrides are great!

As we mentioned before, PrestaShop already has a great system for overrides, and module overrides make it even greater. Overrides truly empower developers and saves a lot of time for everyone.

In the past, overriding module behaviour was a real issue. If using hooks, modifying templates and JavaScript files wasn’t enough, you had to write your own module or rename and modify the module you were trying to change. The updates were instantly lost.

Luckily, now it is possible to override module classes and change the behaviours right at their sources.

Modules overrides have not been documented very well, so not many of you may know about it. Hopefully this gave you some clearance on how to use them.