Yii - Dependency Injection

A DI(dependency injection) container is an object that knows how to instantiate and configure objects. Yii provides the DI container via the yiidiContainer class.

It supports the following kinds of DI −

Setter and property injection

PHP callable injection

Constructor injection

Controller action injection

The DI container supports constructor injection with the help of type hints −

class Object1 {
   pubpc function __construct(Object2 $object2) {

   }
}
$object1 = $container->get( Object1 );
// which is equivalent to the following:
$object2 = new Object2;
$object1 = new Object1($object2);

Property and setter injections are supported through configurations −

<?php
   use yiiaseObject;
   class MyObject extends Object {
      pubpc $var1;
      private $_var2;
      pubpc function getVar2() {
         return $this->_var2;
      }
      pubpc function setVar2(MyObject2 $var2) {
         $this->_var2 = $var2;
      }
   }
   $container->get( MyObject , [], [
       var1  => $container->get( MyOtherObject ),
       var2  => $container->get( MyObject2 ),
   ]);
?>

In case of the PHP callable injection, the container will use a registered PHP callback to build new instances of a class −

$container->set( Object1 , function () {
   $object1 = new Object1(new Object2);
   return $object1;
});
$object1 = $container->get( Object1 );

Controller action injection is a type of DI where dependencies are declared using the type hints. It is useful for keeping the MVC controllers spm pght-weighted and spm −

pubpc function actionSendToAdmin(EmailVapdator $vapdator, $email) {
   if ($vapdator->vapdate($email)) {
      // sending email
   }
}

You can use the yiidbContainer::set() method to register dependencies −

<?php
   $container = new yiidiContainer;
   // register a class name as is. This can be skipped.
   $container->set( yiidbConnection );
   // register an apas name. You can use $container->get( MyObject )
   // to create an instance of Connection
   $container->set( MyObject ,  yiidbConnection );
   // register an interface
   // When a class depends on the interface, the corresponding class
   // will be instantiated as the dependent object
   $container->set( yiimailMailInterface ,  yiiswiftmailerMailer );
   // register an apas name with class configuration
   // In this case, a "class" element is required to specify the class
   $container->set( db , [
       class  =>  yiidbConnection ,
       dsn  =>  mysql:host=127.0.0.1;dbname = helloworld ,
       username  =>  vladimir ,
       password  =>  12345 ,
       charset  =>  utf8 ,
   ]);
   // register a class with configuration. The configuration
   // will be appped when the class is instantiated by get()
   $container->set( yiidbConnection , [
       dsn  =>  mysql:host=127.0.0.1;dbname = helloworld ,
       username  =>  vladimir ,
       password  =>  12345 ,
       charset  =>  utf8 ,
   ]);
   // register a PHP callable
   // The callable will be executed each time when $container->get( db ) is called
   $container->set( db , function ($container, $params, $config) {
      return new yiidbConnection($config);
   });
   // register a component instance
   // $container->get( pageCache ) will return the same instance each time when it 
      //is called
   $container->set( pageCache , new FileCache);
?>

Using the DI

Step 1 − Inside the components folder create a file called MyInterface.php with the following code.

<?php
   namespace appcomponents;
   interface MyInterface {
      pubpc function test();
   }
?>

Step 2 − Inside the components folder, create two files.

First.php −

<?php
   namespace appcomponents;
   use appcomponentsMyInterface;
   class First implements MyInterface {
      pubpc function test() {
         echo "First class <br>";
      }
   }
?>

Second.php −

<?php
   appcomponents;
   use appcomponentsMyInterface;
      class Second implements MyInterface {
      pubpc function test() {
         echo "Second class <br>";
      }
   }
?>

Step 3 − Now, add an actionTestInterface to the SiteController.

pubpc function actionTestInterface() {
   $container = new yiidiContainer();
   $container->set
      ("appcomponentsMyInterface","appcomponentsFirst");
   $obj = $container->get("appcomponentsMyInterface");
   $obj->test(); // print "First class"
   $container->set
      ("appcomponentsMyInterface","appcomponentsSecond");
   $obj = $container->get("appcomponentsMyInterface");
   $obj->test(); // print "Second class"
}

Step 4 − Go to http://localhost:8080/index.php?r=site/test-interface you should see the following.

This approach is convenient as we can set classes in one place and other code will use new classes automatically.