Upgrading from Version 1.1

There are many differences between versions 1.1 and 2.0 of Yii as the framework was completely rewritten for 2.0. As a result, upgrading from version 1.1 is not as trivial as upgrading between minor versions. In this guide you'll find the major differences between the two versions.

If you have not used Yii 1.1 before, you can safely skip this section and turn directly to "Getting started".

Please note that Yii 2.0 introduces more new features than are covered in this summary. It is highly recommended that you read through the whole definitive guide to learn about them all. Chances are that some features you previously had to develop for yourself are now part of the core code.

Installation

Yii 2.0 fully embraces Composer, the de facto PHP package manager. Installation of the core framework, as well as extensions, are handled through Composer. Please refer to the Installing Yii section to learn how to install Yii 2.0. If you want to create new extensions, or turn your existing 1.1 extensions into 2.0-compatible extensions, please refer to the Creating Extensions section of the guide.

PHP Requirements

Yii 2.0 requires PHP 5.4 or above, which is a huge improvement over PHP version 5.2 that is required by Yii 1.1. As a result, there are many differences on the language level that you should pay attention to. Below is a summary of the major changes regarding PHP:

Namespace

The most obvious change in Yii 2.0 is the use of namespaces. Almost every core class is namespaced, e.g., yii\web\Request. The "C" prefix is no longer used in class names. The naming scheme now follows the directory structure. For example, yii\web\Request indicates that the corresponding class file is web/Request.php under the Yii framework folder.

(You can use any core class without explicitly including that class file, thanks to the Yii class loader.)

Component and Object

Yii 2.0 breaks the CComponent class in 1.1 into two classes: yii\base\Object and yii\base\Component. The Object class is a lightweight base class that allows defining object properties via getters and setters. The Component class extends from Object and supports events and behaviors.

If your class does not need the event or behavior feature, you should consider using Object as the base class. This is usually the case for classes that represent basic data structures.

Object Configuration

The Object class introduces a uniform way of configuring objects. Any descendant class of Object should declare its constructor (if needed) in the following way so that it can be properly configured:

class MyClass extends \yii\base\Object
{
    public function __construct($param1, $param2, $config = [])
    {
        // ... initialization before configuration is applied

        parent::__construct($config);
    }

    public function init()
    {
        parent::init();

        // ... initialization after configuration is applied
    }
}

In the above, the last parameter of the constructor must take a configuration array that contains name-value pairs for initializing the properties at the end of the constructor. You can override the init() method to do initialization work that should be done after the configuration has been applied.

By following this convention, you will be able to create and configure new objects using a configuration array:

$object = Yii::createObject([
    'class' => 'MyClass',
    'property1' => 'abc',
    'property2' => 'cde',
], [$param1, $param2]);

More details about configurations can be found in the Configurations section.

Events

In Yii 1, events were created by defining an on-method (e.g., onBeforeSave). In Yii 2, you can now use any event name. You trigger an event by calling the trigger() method:

$event = new \yii\base\Event;
$component->trigger($eventName, $event);

To attach a handler to an event, use the on() method:

$component->on($eventName, $handler);
// To detach the handler, use:
// $component->off($eventName, $handler);

There are many enhancements to the event features. For more details, please refer to the Events section.

Path Aliases

Yii 2.0 expands the usage of path aliases to both file/directory paths and URLs. Yii 2.0 also now requires an alias name to start with the @ character, to differentiate aliases from normal file/directory paths or URLs. For example, the alias @yii refers to the Yii installation directory. Path aliases are supported in most places in the Yii core code. For example, yii\caching\FileCache::$cachePath can take both a path alias and a normal directory path.

A path alias is also closely related to a class namespace. It is recommended that a path alias be defined for each root namespace, thereby allowing you to use Yii class autoloader without any further configuration. For example, because @yii refers to the Yii installation directory, a class like yii\web\Request can be autoloaded. If you use a third party library, such as the Zend Framework, you may define a path alias @Zend that refers to that framework's installation directory. Once you've done that, Yii will be able to autoload any class in that Zend Framework library, too.

More on path aliases can be found in the Aliases section.

Views

The most significant change about views in Yii 2 is that the special variable $this in a view no longer refers to the current controller or widget. Instead, $this now refers to a view object, a new concept introduced in 2.0. The view object is of type yii\web\View, which represents the view part of the MVC pattern. If you want to access the controller or widget in a view, you can use $this->context.

To render a partial view within another view, you use $this->render(), not $this->renderPartial(). The call to render also now has to be explicitly echoed, as the render() method returns the rendering result, rather than directly displaying it. For example:

echo $this->render('_item', ['item' => $item]);

Besides using PHP as the primary template language, Yii 2.0 is also equipped with official support for two popular template engines: Smarty and Twig. The Prado template engine is no longer supported. To use these template engines, you need to configure the view application component by setting the View::$renderers property. Please refer to the Template Engines section for more details.

Models

Yii 2.0 uses yii\base\Model as the base model, similar to CModel in 1.1. The class CFormModel has been dropped entirely. Instead, in Yii 2 you should extend yii\base\Model to create a form model class.

Yii 2.0 introduces a new method called scenarios() to declare supported scenarios, and to indicate under which scenario an attribute needs to be validated, can be considered as safe or not, etc. For example:

public function scenarios()
{
    return [
        'backend' => ['email', 'role'],
        'frontend' => ['email', '!role'],
    ];
}

In the above, two scenarios are declared: backend and frontend. For the backend scenario, both the email and role attributes are safe, and can be massively assigned. For the frontend scenario, email can be massively assigned while role cannot. Both email and role should be validated using rules.

The rules() method is still used to declare the validation rules. Note that due to the introduction of scenarios(), there is no longer an unsafe validator.

In most cases, you do not need to override scenarios() if the rules() method fully specifies the scenarios that will exist, and if there is no need to declare unsafe attributes.

To learn more details about models, please refer to the Models section.

Controllers

Yii 2.0 uses yii\web\Controller as the base controller class, which is similar to CController in Yii 1.1. yii\base\Action is the base class for action classes.

The most obvious impact of these changes on your code is that a controller action should return the content that you want to render instead of echoing it:

public function actionView($id)
{
    $model = \app\models\Post::findOne($id);
    if ($model) {
        return $this->render('view', ['model' => $model]);
    } else {
        throw new \yii\web\NotFoundHttpException;
    }
}

Please refer to the Controllers section for more details about controllers.

Widgets

Yii 2.0 uses yii\base\Widget as the base widget class, similar to CWidget in Yii 1.1.

To get better support for the framework in IDEs, Yii 2.0 introduces a new syntax for using widgets. The static methods begin(), end(), and widget() have been introduced, to be used like so:

use yii\widgets\Menu;
use yii\widgets\ActiveForm;

// Note that you have to "echo" the result to display it
echo Menu::widget(['items' => $items]);

// Passing an array to initialize the object properties
$form = ActiveForm::begin([
    'options' => ['class' => 'form-horizontal'],
    'fieldConfig' => ['inputOptions' => ['class' => 'input-xlarge']],
]);
... form input fields here ...
ActiveForm::end();

Please refer to the Widgets section for more details.

Themes

Themes work completely differently in 2.0. They are now based on a path mapping mechanism that maps a source view file path to a themed view file path. For example, if the path map for a theme is ['/web/views' => '/web/themes/basic'], then the themed version for the view file /web/views/site/index.php will be /web/themes/basic/site/index.php. For this reason, themes can now be applied to any view file, even a view rendered outside of the context of a controller or a widget.

Also, there is no more CThemeManager component. Instead, theme is a configurable property of the view application component.

Please refer to the Theming section for more details.

Console Applications

Console applications are now organized as controllers, like Web applications. Console controllers should extend from yii\console\Controller, similar to CConsoleCommand in 1.1.

To run a console command, use yii <route>, where <route> stands for a controller route (e.g. sitemap/index). Additional anonymous arguments are passed as the parameters to the corresponding controller action method, while named arguments are parsed according to the declarations in yii\console\Controller::options().

Yii 2.0 supports automatic generation of command help information from comment blocks.

Please refer to the Console Commands section for more details.

I18N

Yii 2.0 removes the built-in date formatter and number formatter pieces in favor of the PECL intl PHP module.

Message translation is now performed via the i18n application component. This component manages a set of message sources, which allows you to use different message sources based on message categories.

Please refer to the Internationalization section for more details.

Action Filters

Action filters are implemented via behaviors now. To define a new, custom filter, extend from yii\base\ActionFilter. To use a filter, attach the filter class to the controller as a behavior. For example, to use the yii\filters\AccessControl filter, you would have the following code in a controller:

public function behaviors()
{
    return [
        'access' => [
            'class' => 'yii\filters\AccessControl',
            'rules' => [
                ['allow' => true, 'actions' => ['admin'], 'roles' => ['@']],
            ],
        ],
    ];
}

Please refer to the Filtering section for more details.

Assets

Yii 2.0 introduces a new concept called asset bundle that replaces the script package concept found in Yii 1.1.

An asset bundle is a collection of asset files (e.g. JavaScript files, CSS files, image files, etc.) within a directory. Each asset bundle is represented as a class extending yii\web\AssetBundle. By registering an asset bundle via yii\web\AssetBundle::register(), you make the assets in that bundle accessible via the Web. Unlike in Yii 1, the page registering the bundle will automatically contain the references to the JavaScript and CSS files specified in that bundle.

Please refer to the Managing Assets section for more details.

Helpers

Yii 2.0 introduces many commonly used static helper classes, including.

Please refer to the Helper Overview section for more details.

Forms

Yii 2.0 introduces the field concept for building a form using yii\widgets\ActiveForm. A field is a container consisting of a label, an input, an error message, and/or a hint text. A field is represented as an ActiveField object. Using fields, you can build a form more cleanly than before:

<?php $form = yii\widgets\ActiveForm::begin(); ?>
    <?= $form->field($model, 'username') ?>
    <?= $form->field($model, 'password')->passwordInput() ?>
    <div class="form-group">
        <?= Html::submitButton('Login') ?>
    </div>
<?php yii\widgets\ActiveForm::end(); ?>

Please refer to the Creating Forms section for more details.

Query Builder

In 1.1, query building was scattered among several classes, including CDbCommand, CDbCriteria, and CDbCommandBuilder. Yii 2.0 represents a DB query in terms of a Query object that can be turned into a SQL statement with the help of QueryBuilder behind the scene. For example:

$query = new \yii\db\Query();
$query->select('id, name')
      ->from('user')
      ->limit(10);

$command = $query->createCommand();
$sql = $command->sql;
$rows = $command->queryAll();

Best of all, such query building methods can also be used when working with Active Record.

Please refer to the Query Builder section for more details.

Active Record

Yii 2.0 introduces a lot of changes to Active Record. The two most obvious ones involve query building and relational query handling.

The CDbCriteria class in 1.1 is replaced by yii\db\ActiveQuery in Yii 2. That class extends from yii\db\Query, and thus inherits all query building methods. You call yii\db\ActiveRecord::find() to start building a query:

// To retrieve all *active* customers and order them by their ID:
$customers = Customer::find()
    ->where(['status' => $active])
    ->orderBy('id')
    ->all();

To declare a relation, simply define a getter method that returns an ActiveQuery object. The property name defined by the getter represents the relation name. For example, the following code declares an orders relation (in 1.1, you would have to declare relations in a central place relations()):

class Customer extends \yii\db\ActiveRecord
{
    public function getOrders()
    {
        return $this->hasMany('Order', ['customer_id' => 'id']);
    }
}

Now you can use $customer->orders to access a customer's orders from the related table. You can also use the following code to perform an on-the-fly relational query with a customized query condition:

$orders = $customer->getOrders()->andWhere('status=1')->all();

When eager loading a relation, Yii 2.0 does it differently from 1.1. In particular, in 1.1 a JOIN query would be created to select both the primary and the relational records. In Yii 2.0, two SQL statements are executed without using JOIN: the first statement brings back the primary records and the second brings back the relational records by filtering with the primary keys of the primary records.

Instead of returning ActiveRecord objects, you may chain the asArray() method when building a query to return a large number of records. This will cause the query result to be returned as arrays, which can significantly reduce the needed CPU time and memory if large number of records . For example:

$customers = Customer::find()->asArray()->all();

Another change is that you can't define attribute default values through public properties anymore. If you need those, you should set them in the init method of your record class.

public function init()
{
    parent::init();
    $this->status = self::STATUS_NEW;
}

There were some problems with overriding the constructor of an ActiveRecord class in 1.1. These are not present in version 2.0 anymore. Note that when adding parameters to the constructor you might have to override yii\db\ActiveRecord::instantiate().

There are many other changes and enhancements to Active Record. Please refer to the Active Record section for more details.

Active Record Behaviors

In 2.0, we have dropped the base behavior class CActiveRecordBehavior. If you want to create an Active Record Behavior, you will have to extend directly from yii\base\Behavior. If the behavior class needs to respond to some events of the owner, you have to override the events() method like the following:

namespace app\components;

use yii\db\ActiveRecord;
use yii\base\Behavior;

class MyBehavior extends Behavior
{
    // ...

    public function events()
    {
        return [
            ActiveRecord::EVENT_BEFORE_VALIDATE => 'beforeValidate',
        ];
    }

    public function beforeValidate($event)
    {
        // ...
    }
}

User and IdentityInterface

The CWebUser class in 1.1 is now replaced by yii\web\User, and there is no more CUserIdentity class. Instead, you should implement the yii\web\IdentityInterface which is much more straightforward to use. The advanced project template provides such an example.

Please refer to the Authentication, Authorization, and Advanced Project Template sections for more details.

URL Management

URL management in Yii 2 is similar to that in 1.1. A major enhancement is that URL management now supports optional parameters. For example, if you have a rule declared as follows, then it will match both post/popular and post/1/popular. In 1.1, you would have had to use two rules to achieve the same goal.

[
    'pattern' => 'post/<page:\d+>/<tag>',
    'route' => 'post/index',
    'defaults' => ['page' => 1],
]

Please refer to the Url manager docs section for more details.

An important change in the naming convention for routes is that camel case names of controllers and actions are now converted to lower case where each word is separated by a hypen, e.g. the controller id for the CamelCaseController will be camel-case. See the section about controller IDs and action IDs for more details.

Using Yii 1.1 and 2.x together

If you have legacy Yii 1.1 code that you want to use together with Yii 2.0, please refer to the Using Yii 1.1 and 2.0 Together section.