behaviors.md

Behaviors

A behavior (also knows as mixin) can be used to enhance the functionality of an existing component without modifying the component's code. In particular, a behavior can "inject" its public methods and properties into the component, making them directly accessible via the component itself. A behavior can also respond to events triggered in the component, thus intercepting the normal code execution. Unlike PHP's traits, behaviors can be attached to classes at runtime.

Using behaviors

A behavior can be attached to any class that extends from [[yii\base\Component]] either from code or via application config.

Attaching behaviors via behaviors method

In order to attach a behavior to a class you can implement the behaviors method of the component. As an example, Yii provides the [[yii\behaviors\TimestampBehavior]] behavior for automatically updating timestamp fields when saving an [[yii\db\ActiveRecord|Active Record]] model:

use yii\behaviors\TimestampBehavior;

class User extends ActiveRecord
{
    // ...

    public function behaviors()
    {
        return [
            'timestamp' => [
                'class' => TimestampBehavior::className(),
                'attributes' => [
                    ActiveRecord::EVENT_BEFORE_INSERT => ['created_at', 'updated_at'],
                    ActiveRecord::EVENT_BEFORE_UPDATE => 'updated_at',
                ],
            ],
        ];
    }
}

In the above, the name timestamp can be used to reference the behavior through the component. For example, $user->timestamp gives the attached timestamp behavior instance. The corresponding array is the configuration used to create the [[yii\behaviors\TimestampBehavior|TimestampBehavior]] object.

Besides responding to the insertion and update events of ActiveRecord, TimestampBehavior also provides a method touch() that can assign the current timestamp to a specified attribute. As aforementioned, you can access this method directly through the component, like the following:

$user->touch('login_time');

If you do not need to access a behavior object, or the behavior does not need customization, you can also use the following simplified format when specifying the behavior,

use yii\behaviors\TimestampBehavior;

class User extends ActiveRecord
{
    // ...

    public function behaviors()
    {
        return [
            TimestampBehavior::className(),
            // or the following if you want to access the behavior object
            // 'timestamp' => TimestampBehavior::className(),
        ];
    }
}

Attaching behaviors dynamically

Another way to attach a behavior to a component is calling attachBehavior method like the followig:

$component = new MyComponent();
$component->attachBehavior();

Attaching behaviors from config

One can attach a behavior to a component when configuring it with a configuration array. The syntax is like the following:

return [
    // ...
    'components' => [
        'myComponent' => [
            // ...
            'as tree' => [
                'class' => 'Tree',
                'root' => 0,
            ],
        ],
    ],
];

In the config above as tree stands for attaching a behavior named tree, and the array will be passed to [[\Yii::createObject()]] to create the behavior object.

Creating your own behaviors

To create your own behavior, you must define a class that extends [[yii\base\Behavior]].

namespace app\components;

use yii\base\Behavior;

class MyBehavior extends Behavior
{
}

To make it customizable, like [[yii\behaviors\TimestampBehavior]], add public properties:

namespace app\components;

use yii\base\Behavior;

class MyBehavior extends Behavior
{
    public $attr;
}

Now, when the behavior is used, you can set the attribute to which you'd want the behavior to be applied:

namespace app\models;

use yii\db\ActiveRecord;

class User extends ActiveRecord
{
    // ...

    public function behaviors()
    {
        return [
            'mybehavior' => [
                'class' => 'app\components\MyBehavior',
                'attr' => 'member_type'
            ],
        ];
    }
}

Behaviors are normally written to take action when certain events occur. Below we're implementing events method to assign event handlers:

namespace app\components;

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

class MyBehavior extends Behavior
{
    public $attr;

    public function events()
    {
        return [
            ActiveRecord::EVENT_BEFORE_INSERT => 'beforeInsert',
            ActiveRecord::EVENT_BEFORE_UPDATE => 'beforeUpdate',
        ];
    }

    public function beforeInsert() {
        $model = $this->owner;
        // Use $model->$attr
    }

    public function beforeUpdate() {
        $model = $this->owner;
        // Use $model->$attr
    }
}