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.
A behavior can be attached to any class that extends from [[yii\base\Component]] either from code or via application config.
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(),
];
}
}
Another way to attach a behavior to a component is calling attachBehavior
method like the followig:
$component = new MyComponent();
$component->attachBehavior();
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.
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
}
}