yii2-bootstrap/docs/guide/upgrade-from-v1.md

Upgrading from Yii 1.1

In this chapter, we list the major changes introduced in Yii 2.0 since version 1.1. We hope this list will make it easier for you to upgrade from Yii 1.1 and quickly master Yii 2.0 based on your existing Yii knowledge.

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 of the namespaces follows the directory structure. For example, yii\web\Request indicates the corresponding class file is web/Request.php under the Yii framework folder. You can use any core class without explicitly include 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: Object and Component. The Object class is a lightweight base class that allows defining class properties via getters and setters. The Component class extends from Object and supports the event feature and the behavior feature.

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\Object
{
    public function __construct($param1, $param2, $config = array())
    {
        // ... 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 which 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 is applied.

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

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

Events

There is no longer the need to define an on-method in order to define an event in Yii 2.0. Instead, you can use whatever event names. To attach a handler to an event, you should use the on method now:

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

When you attach a handler, you can now associate it with some parameters which can be later accessed via the event parameter by the handler:

$component->on($eventName, $handler, $params);

Because of this change, you can now use "global" events. Simply trigger and attach handlers to an event of the application instance:

Yii::$app->on($eventName, $handler);
....
// this will trigger the event and cause $handler to be invoked.
Yii::$app->trigger($eventName);

Path Alias

Yii 2.0 expands the usage of path aliases to both file/directory paths and URLs. An alias must start with a @ character so that it can be differentiated from file/directory paths and 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, FileCache::cachePath can take both a path alias and a normal directory path.

Path alias is also closely related with class namespaces. It is recommended that a path alias defined for each root namespace so that you can 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 by Yii. If you use a third party library such as Zend Framework, you may define a path alias @Zend which refers to its installation directory. And Yii will be able to autoload any class in this library.

View

Yii 2.0 introduces a View class to represent the view part in the MVC pattern. It can be configured globally through the "view" application component. It is also accessible in any view file via $this. This is one of the biggest changes compared to 1.1: $this in a view file no longer refers to the controller or widget object. It refers to the view object that is used to render the view file. To access the controller or the widget object, you have to use $this->context now.

Because you can access the view object through the "view" application component, you can now render a view file like the following anywhere in your code, not necessarily in controllers or widgets:

$content = Yii::$app->view->renderFile($viewFile, $params);
// You can also explicitly create a new View instance to do the rendering
// $view = new View;
// $view->renderFile($viewFile, $params);

Also, there is no more CClientScript in Yii 2.0. The View class has taken over its role with significant improvements. For more details, please see the "assets" subsection.

While Yii 2.0 continues to use PHP as its main template language, it comes with built-in support for two popular template engines: Smarty and Twig. The Prado template engine is no longer supported. To use these template engines, you just need to use tpl as the file extension for your Smarty views, or twig for Twig views. You may also configure the View::renderers property to use other template engines.

Models

A model is now associated with a form name returned its formName() method. This is mainly used when using HTML forms to collect user inputs for a model. Previously in 1.1, this is usually hardcoded as the class name of the model.

Yii 2.0 introduces a new method called scenarios() to declare which attributes require validation under which scenario. Child classes should overwrite scenarios() to return a list of scenarios and the corresponding attributes that need to be validated when validate() is called. For example,

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

This method also determines which attributes are safe and which are not. In particular, given a scenario, if an attribute appears in the corresponding attribute list in scenarios() and the name is not prefixed with !, it is considered safe.

Because of the above change, Yii 2.0 no longer has "safe" and "unsafe" validators.

If your model only has one scenario (very common), you do not have to overwrite scenarios(), and everything will still work like the 1.1 way.

Controllers

The render() and renderPartial() methods now return the rendering results instead of directly sending them out. You have to echo them explicitly, e.g., echo $this->render(...);.

A new method called populate() is introduced to simplify the data population from user inputs to a model. For example,

$post = new Post;
if ($this->populate($_POST, $model)) {...}
// which is equivalent to:
if (isset($_POST['Post'])) {
    $post->attributes = $_POST['Post'];
}

Themes

Theme works completely different in 2.0. It is now based on a path map to "translate" a source view into a themed view. For example, if the path map for a theme is array('/www/views' => '/www/themes/basic'), then the themed version for a view file /www/views/site/index.php will be /www/themes/basic/site/index.php.

For this reason, theme can now be applied to any view file, even if a view rendered outside of the context of a controller or a widget.

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

Console Applications

Console applications are now composed by controllers, too, like Web applications. In fact, console controllers and Web controllers share the same base controller class.

Each console controller is like CConsoleCommand in 1.1. It consists of one or several actions. You use the yiic <route> command to execute a console command, 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, and named arguments are treated as global options declared in globalOptions().

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

I18N

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

Message translation is still supported, but managed via the "i18n" application component. The component manages a set of message sources, which allows you to use different message sources based on message categories. For more information, see the class documentation for I18N.

The message translation method is changed by merging the message category into the message being translated. For example, Yii::t('yii|message to be translated').

Action Filters

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

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

Assets

Yii 2.0 introduces a new concept called asset bundle. It is a bit similar to script packages (managed by CClientScript) in 1.1, but with better support.

An asset bundle is a collection of asset files (e.g. JavaScript files, CSS files, image files, etc.) under a directory. By registering an asset bundle via View::registerAssetBundle(), you will be able to make the assets in that bundle accessible via Web, and the current page will automatically contain references to the JavaScript and CSS files in that bundle.

Static Helpers

Yii 2.0 introduces many commonly used static helper classes, such as Html, ArrayHelper, StringHelper. These classes are designed to be easily extended. Note that static classes are usually hard to be extended because of the fixed class name references. But Yii 2.0 introduces the class map (via Yii::$classMap) to overcome this difficulty.

ActiveForm

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

<?php $form = $this->beginWidget('yii\widgets\ActiveForm'); ?>
	<?php echo $form->field($model, 'username')->textInput(); ?>
	<?php echo $form->field($model, 'password')->passwordInput(); ?>
	<div class="form-actions">
		<?php echo Html::submitButton('Login'); ?>
	</div>
<?php $this->endWidget(); ?>

Query Builder

In 1.1, query building is scattered among several classes, including CDbCommand, CDbCriteria, and CDbCommandBuilder. Yii 2.0 uses Query to represent a DB query and QueryBuilder to generate SQL statements from query objects. For example,

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

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

Best of all, such query building methods can be used together with ActiveRecord, as explained in the next sub-section.

ActiveRecord

ActiveRecord has undergone significant changes in Yii 2.0. The most important one is about relational ActiveRecord query. In 1.1, you have to declare the relations in the relations() method. In 2.0, this is done via getter methods that return an ActiveQuery object. For example, the following method declares an "orders" relation:

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

You can use $customer->orders to access the customer's orders. You can also use $customer->getOrders()->andWhere('status=1')->all() to perform on-the-fly relational query with customized query conditions.

When loading relational records in an eager way, Yii 2.0 does it differently from 1.1. In particular, in 1.1 a JOIN query would be used to bring both the primary and the relational records; while 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.

Yii 2.0 no longer uses the model() method when performing queries. Instead, you use the find() method like the following:

// to retrieve all *active* customers and order them by their ID:
$customers = Customer::find()
	->where(array('status' => $active))
	->orderBy('id')
	->all();
// return the customer whose PK is 1
$customer = Customer::find(1);

The find() method returns an instance of ActiveQuery which is a subclass of Query. Therefore, you can use all query methods of Query.

Instead of returning ActiveRecord objects, you may call ActiveQuery::asArray() to return results in terms of arrays. This is more efficient and is especially useful when you need to return large number of records. For example,

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

By default, ActiveRecord now only saves dirty attributes. In 1.1, all attributes would be saved to database when you call save(), regardless they are changed or not, unless you explicitly list the attributes to save.

Auto-quoting Table and Column Names

Yii 2.0 supports automatic quoting of database table and column names. A name enclosed within double curly brackets is treated as a table name, and a name enclosed within double square brackets is treated as a column name. They will be quoted according to the database driver being used. For example,

$command = $connection->createCommand('SELECT [[id]] FROM {{posts}}');
echo $command->sql;  // MySQL: SELECT `id` FROM `posts`

This feature is especially useful if you are developing an application that supports different DBMS.

User and Identity

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 Identity interface which is much more straightforward to implement. The bootstrap application provides such an example.

URL Management

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.

array(
	'pattern' => 'post/<page:\d+>/<tag>',
	'route' => 'post/index',
	'defaults' => array('page' => 1),
)

Response

Extensions

Integration with Composer

TBD