How to Build a Module

# Preparation

Before you begin working on a module, you need to decide on a couple things:

Namespace
The root namespace that your module’s classes will live in. (See the PSR-4 (opens new window) autoloading specification for details.) Note that this should not begin with craft\; use something that identifies you (the developer), or the project.
Module ID
Something that uniquely identifies the module within your project. IDs must begin with a letter and contain only lowercase letters, numbers, and dashes, and should be kebab-cased.
The module ID will become the first segment in controller action paths.

When choosing a module ID, avoid names that will conflict with Craft’s core controllers (opens new window) (e.g. app would conflict with AppController.php), as well as any installed plugin handles.

# Set up the basic file structure

To create a module, create a new directory for it somewhere within your Craft project, such as modules/<ModuleID>/. For example, if your module ID is foo, you might set it up like this:

my-project
├── modules
└── foo
    └── Module.php
├── templates
└── ...

# Set up class autoloading

Next up, you need to tell Composer how to find your module’s classes by setting the autoload (opens new window) field in your project’s composer.json file. For example, if your module’s namespace is foo, and it’s located at modules/foo/, this is what you should add:

{
  // ...
  "autoload": {
    "psr-4": {
      "foo\\": "modules/foo/"
    }
  }
}

With that in place, go to your project’s directory in your terminal, and run the following command:

composer dump-autoload -a

That will tell Composer to update its class autoloader script based on your new autoload mapping.

# The Module class

The Module.php file is your module’s entry point for the system. Its init() method is the best place to register event listeners, and any other steps it needs to take to initialize itself.

Use this template as a starting point for your Module.php file:

<?php
namespace foo;

use Craft;

class Module extends \yii\base\Module
{
    public function init()
    {
        // Define a custom alias named after the namespace
        Craft::setAlias('@foo', __DIR__);

        // Set the controllerNamespace based on whether this is a console or web request
        if (Craft::$app->getRequest()->getIsConsoleRequest()) {
            $this->controllerNamespace = 'foo\\console\\controllers';
        } else {
            $this->controllerNamespace = 'foo\\controllers';
        }

        parent::init();

        // Custom initialization code goes here...
    }
}

Replace foo with your module’s actual namespace, and '@foo' with an alias (opens new window) name based on your actual namespace (with any \s converted to /s).

# Initialization

Most initialization logic belongs in your module’s init() method.

However, there are some situations where this doesn’t guarantee a certain part of the application is ready (another plugin, for instance). Conversely, a module that isn’t bootstrapped at the beginning of a request may have init() called too late to listen to craft\web\Application::EVENT_INIT (opens new window), and would never be notified that the app is indeed ready.

In those cases, it’s best to register a callback via craft\base\ApplicationTrait::onInit() (opens new window):

<?php
namespace foo;

use Craft;

class Module extends \yii\base\Module
{
    public function init()
    {
        // ...

        // Defer most setup tasks until Craft is fully initialized:
        Craft::$app->onInit(function() {
            // ...
        });
    }
}

If Craft has already fully initialized, the callback will be invoked immediately.

# Update the application config

You can add your module to your project’s application configuration by listing it in the modules (opens new window) and bootstrap (opens new window) arrays. For example, if your module ID is foo and its Module class name is foo\Module, this is what you should add to config/app.php:




 


 



return [
    // ...
    'modules' => [
        'foo' => foo\Module::class,
    ],
    'bootstrap' => [
        'foo',
    ],
];

If your module doesn’t need to get loaded on every request, you can remove its ID from the bootstrap array. If you end up using any event listeners in your module’s init() method, it should be loaded on every request.

# Further Reading

To learn more about modules, see the Yii documentation (opens new window).