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Behaviors
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=========
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A behavior (also knows as *mixin*) can be used to enhance the functionality of an existing component without modifying the component's
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code. In particular, a behavior can "inject" its own methods and properties into the component, making them directly accessible
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via the component itself. A behavior can also respond to events triggered in the component, thus intercepting the normal
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code execution. Unlike [PHP's traits](http://www.php.net/traits), behaviors can be attached to classes at runtime.
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Using behaviors
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---------------
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A behavior can be attached to any class that extends from [[yii\base\Component]]. In order to attach a behavior to a class,
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the component class must implement the `behaviors`
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method. As an example, Yii provides the [[yii\behaviors\AutoTimestamp|AutoTimestamp]] behavior for automatically updating timestamp
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fields when saving an [[yii\db\ActiveRecord|Active Record]] model:
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```php
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class User extends ActiveRecord
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{
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// ...
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public function behaviors()
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{
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return [
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'timestamp' => [
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'class' => 'yii\behaviors\AutoTimestamp',
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'attributes' => [
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ActiveRecord::EVENT_BEFORE_INSERT => ['created_at', 'updated_at'],
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ActiveRecord::EVENT_BEFORE_UPDATE => 'updated_at',
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],
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],
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];
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}
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}
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```
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In the above, the `class` value is a string representing the fully qualified behavior class name.
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All of the other key-value pairs represent corresponding public properties of the [[yii\behaviors\AutoTimestamp|AutoTimestamp]]
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class, thereby customizing how the behavior functions.
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Creating your own behaviors
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---------------------------
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To create your own behavior, you must define a class that extends [[yii\base\Behavior]].
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```php
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namespace app\components;
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use yii\base\Behavior;
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class MyBehavior extends Behavior
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{
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}
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```
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To make it customizable, like [[yii\behaviors\AutoTimestamp]], add public properties:
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```php
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namespace app\components;
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use yii\base\Behavior;
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class MyBehavior extends Behavior
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{
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public $attr;
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}
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```
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Now, when the behavior is used, you can set the attribute to which you'd want the behavior to be applied:
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```php
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namespace app\models;
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use yii\db\ActiveRecord;
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class User extends ActiveRecord
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{
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// ...
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public function behaviors()
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{
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return [
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'mybehavior' => [
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'class' => 'app\components\MyBehavior',
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'attr' => 'member_type'
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],
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];
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}
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}
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```
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Behaviors are normally written to take action when certain events occur. Below we're implementing `events` method
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to assign event handlers:
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```php
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namespace app\components;
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use yii\base\Behavior;
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use yii\db\ActiveRecord;
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class MyBehavior extends Behavior
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{
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public $attr;
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public function events()
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{
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return [
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ActiveRecord::EVENT_BEFORE_INSERT => 'beforeInsert',
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ActiveRecord::EVENT_BEFORE_UPDATE => 'beforeUpdate',
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];
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}
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public function beforeInsert() {
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$model = $this->owner;
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// Use $model->$attr
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}
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public function beforeUpdate() {
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$model = $this->owner;
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// Use $model->$attr
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}
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}
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```
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