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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 public 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]] either from code or via application
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config.
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### Attaching behaviors via `behaviors` method
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In order to attach a behavior to a class you can implement the `behaviors` method of the component.
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As an example, Yii provides the [[yii\behaviors\TimestampBehavior]] 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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use yii\behaviors\TimestampBehavior;
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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' => TimestampBehavior::className(),
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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 name `timestamp` can be used to reference the behavior through the component. For example, `$user->timestamp`
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gives the attached timestamp behavior instance. The corresponding array is the configuration used to create the
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[[yii\behaviors\TimestampBehavior|TimestampBehavior]] object.
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Besides responding to the insertion and update events of ActiveRecord, `TimestampBehavior` also provides a method `touch()`
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that can assign the current timestamp to a specified attribute. As aforementioned, you can access this method directly
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through the component, like the following:
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```php
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$user->touch('login_time');
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```
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If you do not need to access a behavior object, or the behavior does not need customization, you can also
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use the following simplified format when specifying the behavior,
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```php
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use yii\behaviors\TimestampBehavior;
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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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TimestampBehavior::className(),
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// or the following if you want to access the behavior object
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// 'timestamp' => TimestampBehavior::className(),
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];
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}
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}
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```
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### Attaching behaviors dynamically
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Another way to attach a behavior to a component is calling `attachBehavior` method like the followig:
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```php
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$component = new MyComponent();
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$component->attachBehavior();
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```
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### Attaching behaviors from config
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One can attach a behavior to a component when configuring it with a configuration array. The syntax is like the
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following:
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```php
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return [
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// ...
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'components' => [
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'myComponent' => [
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// ...
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'as tree' => [
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'class' => 'Tree',
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'root' => 0,
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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 config above `as tree` stands for attaching a behavior named `tree`, and the array will be passed to [[\Yii::createObject()]]
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to create the behavior object.
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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\TimestampBehavior]], 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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