A module is an entity that has its own models, views, controllers, and possibly other modules. It is practically an application inside the application.

Step 1 − Create a folder called modules inside your project root. Inside the modules folder, create a folder named hello. This will be the basic folder for our Hello module.

Step 2 − Inside the hello folder, create a file Hello.php with the following code.

<?php
   namespace appmoduleshello;
   class Hello extends yiibaseModule {
      public function init() {
         parent::init();
      }
   }
?>

We have just created a module class. This should be located under the module”s base path. Every time a module is accessed, an instance of the correspondent module class is created. The init() function is for initializing the module”s properties.

Step 3 − Now, add two more directories inside the hello folder − controllers and views. Add a CustomController.php file to the controller’s folder.

<?php
   namespace appmoduleshellocontrollers;
   use yiiwebController;
   class CustomController extends Controller {
      public function actionGreet() {
         return $this->render(''greet'');
      }
   }
?>

When creating a module, a convention is to put the controller classes into the controller’s directory of the module”s base path. We have just defined the actionGreet function, that just returns a greet view.

Views in the module should be put in the views folder of the module”s base path. If views are rendered by a controller, they should be located in the folder corresponding to the controllerID. Add custom folder to the views folder.

Step 4 − Inside the custom directory, create a file called greet.php with the following code.

<h1>Hello world from custom module!</h1>

We have just created a View for our actionGreet. To use this newly created module, we should configure the application. We should add our module to the modules property of the application.

Step 5 − Modify the config/web.php file.

<?php
   $params = require(__DIR__ . ''/params.php'');
   $config = [
      ''id'' => ''basic'',
      ''basePath'' => dirname(__DIR__),
      ''bootstrap'' => [''log''],
      ''components'' => [
         ''request'' => [
            // !!! insert a secret key in the following (if it is empty) - this is
               //required by cookie validation
            ''cookieValidationKey'' => ''ymoaYrebZHa8gURuolioHGlK8fLXCKjO'',
         ],
         ''cache'' => [
            ''class'' => ''yiicachingFileCache'',
         ],
         ''user'' => [
            ''identityClass'' => ''appmodelsUser'',
            ''enableAutoLogin'' => true,
         ],
         ''errorHandler'' => [
            ''errorAction'' => ''site/error'',
         ],
         ''mailer'' => [
            ''class'' => ''yiiswiftmailerMailer'',
            // send all mails to a file by default. You have to set
            // ''useFileTransport'' to false and configure a transport
            // for the mailer to send real emails.
            ''useFileTransport'' => true,
         ],
         ''log'' => [
            ''traceLevel'' => YII_DEBUG ? 3 : 0,
            ''targets'' => [
               [
                  ''class'' => ''yiilogFileTarget'',
                  ''levels'' => [''error'', ''warning''],
               ],
            ],
         ],
         ''db'' => require(__DIR__ . ''/db.php''),
      ],
      ''modules'' => [
         ''hello'' => [
            ''class'' => ''appmoduleshelloHello'', 
         ],
      ],
      ''params'' => $params,
   ];
   if (YII_ENV_DEV) {
      // configuration adjustments for ''dev'' environment
      $config[''bootstrap''][] = ''debug'';
      $config[''modules''][''debug''] = [
         ''class'' => ''yiidebugModule'',
      ];
      $config[''bootstrap''][] = ''gii'';
      $config[''modules''][''gii''] = [
         ''class'' => ''yiigiiModule'',
      ];
   }
   return $config;
?>

A route for a module”s controller must begin with the module ID followed by the controller ID and action ID.

Step 6 − To run the actionGreet in our application, we should use the following route.

hello/custom/greet

Where hello is a module ID, custom is a controller ID and greet is an action ID.

Step 7 − Now, type http://localhost:8080/index.php?r=hello/custom/greet and you will see the following output.

Important Points

Modules should −

• Be used in large applications. You should divide its features into several groups. Each feature group can be developed as a module.

• Be reusable. Some commonly used features, as SEO management or blog management, can be developed as modules, so that you can easily reuse them in future projects.