There are many differences between versions 1.1 and 2.0 of the 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.
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.
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 Starting from Basic App 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.
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:
- Namespaces.
- Anonymous functions.
- Short array syntax
[...elements...]is used instead ofarray(...elements...). - Short echo tags
<?=are used in view files. This is safe to use starting from PHP 5.4. - SPL classes and interfaces.
- Late Static Bindings.
- Date and Time.
- Traits.
- intl. Yii 2.0 makes use of the
intlPHP extension to support internationalization features.
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.)
Yii 2.0 breaks the CComponent class in 1.1 into two classes: [[yii\base\Object]] and [[yii\base\Component]].
The [[yii\base\Object|Object]] class is a lightweight base class that allows defining object properties
via getters and setters. The [[yii\base\Component|Component]] class extends from [[yii\base\Object|Object]] and supports
events and behaviors.
If your class does not need the event or behavior feature, you should consider using [[yii\base\Object|Object]] as the base class. This is usually the case for classes that represent basic data structures.
The [[yii\base\Object|Object]] class introduces a uniform way of configuring objects. Any descendant class of [[yii\base\Object|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 [[yii\base\Object::init()|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 Object Configurations section.
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 [[yii\base\Component::trigger()|trigger()]] method:
$event = new \yii\base\Event;
$component->trigger($eventName, $event);To attach a handler to an event, use the [[yii\base\Component::on()|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.
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 the 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 Path Aliases section.
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. In 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' => $item]);Besides using PHP as the primary template language, Yii 2.0 is also equipped with official
support for two popular template engines: Smarty and Twig. The Prado template engine is no longer supported.
To use these template engines, you need to configure the view application component by setting the
[[yii\base\View::$renderers|View::$renderers]] property. Please refer to the Template Engines
section for more details.
Yii 2.0 uses [[yii\base\Model]] as the base model, similar to CModel in 1.1.
The class CFormModel has been dropped entirely. Instead, in Yii 2 you should extend [[yii\base\Model]] to create a form model class.
Yii 2.0 introduces a new method called [[yii\base\Model::scenarios()|scenarios()]] to declare supported scenarios, and to indicate under which scenario an attribute needs to be validated, can be considered as safe or not, etc. For example:
public function scenarios()
{
return [
'backend' => ['email', 'role'],
'frontend' => ['email', '!name'],
];
}In the above, two scenarios are declared: backend and frontend. For the backend scenario, both the
email and role attributes are safe, and can be massively assigned. For the frontend scenario,
email can be massively assigned while role cannot. Both email and role should be validated using rules.
The [[yii\base\Model::rules()|rules()]] method is still used to declare the validation rules. Note that due to the introduction of [[yii\base\Model::scenarios()|scenarios()]], there is no longer an unsafe validator.
In most cases, you do not need to override [[yii\base\Model::scenarios()|scenarios()]]
if the [[yii\base\Model::rules()|rules()]] method fully specifies the scenarios that will exist, and if there is no need to declare
unsafe attributes.
To learn more details about models, please refer to the Models section.
Yii 2.0 uses [[yii\web\Controller]] as the base controller class, similar to CWebController in Yii 1.1.
[[yii\base\Action]] is the base class for action classes.
The most obvious impact of these changes on your code is that a controller action should return the content that you want to render instead of echoing it:
public function actionView($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.
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 [[yii\base\Widget::begin()|begin()]], [[yii\base\Widget::end()|end()]], and [[yii\base\Widget::widget()|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 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 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.
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 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.
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.
Yii 2.0 introduces many commonly used static helper classes, including.
- [[yii\helpers\Html]]
- [[yii\helpers\ArrayHelper]]
- [[yii\helpers\StringHelper]]
- [[yii\helpers\FileHelper]]
- [[yii\helpers\Json]]
- [[yii\helpers\Security]]
Please refer to the Helper Overview section for more details.
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 [[yii\widgets\ActiveField|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.
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 [[yii\db\Query|Query]] object
that can be turned into a SQL statement with the help of [[yii\db\QueryBuilder|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.
Yii 2.0 introduces a lot of changes to Active Record. Two most obvious ones are query building and relational query handling.
The CDbCriteria class in 1.1 is replaced by [[yii\db\ActiveQuery]] which extends from [[yii\db\Query]] and thus
inherits all query building methods. You call [[yii\db\ActiveRecord::find()]] to start building a query.
For example,
// to retrieve all *active* customers and order them by their ID:
$customers = Customer::find()
->where(['status' => $active])
->orderBy('id')
->all();To declare a relation, you simply define a getter method that returns an [[yii\db\ActiveQuery|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']);
}
}You can use $customer->orders to access the customer's orders. You can also use the following code
to perform on-the-fly relational query with customized query conditions:
$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 bring both the primary and the relational records; in 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 [[yii\db\ActiveRecord|ActiveRecord]] objects, you may chain the [[yii\db\ActiveQuery::asArray()|asArray()]] method when building a query to return 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();There are many other changes and enhancements to Active Record. Please refer to the Active Record section for more details.
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 implement. The advanced application template provides such an example.
URL management is similar to 1.1. A major enhancement is that it now supports optional
parameters. For example, if you have rule declared as follows, then it will match
both post/popular and post/1/popular. In 1.1, you would have to use two rules to achieve
the same goal.
[
'pattern' => 'post/<page:\d+>/<tag>',
'route' => 'post/index',
'defaults' => ['page' => 1],
]More details in the Url manager docs.
If you have legacy Yii 1.1 code and you want to use it together with Yii 2.0, please refer to the Using Yii 1.1 and 2.0 Together section.