# AttributeBehavior

> AttributeBehavior automatically assigns a specified value to one or multiple attributes of an ActiveRecord object when certain events happen.

[API reference](/docs/api/index.md) › [yii](/docs/api/yii/index.md) › [behaviors](/docs/api/yii/behaviors/index.md) › AttributeBehavior

| class | `yii\behaviors\AttributeBehavior` |
| --- | --- |
| Extends | [`yii\base\Behavior`](/docs/api/yii/base/behavior/index.md) » [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| Implements | [`yii\base\Configurable`](/docs/api/yii/base/configurable/index.md) |
| Since | 2.0 |
| Source | [`framework/behaviors/AttributeBehavior.php`](https://github.com/yiisoft/yii2/blob/22.0/framework/behaviors/AttributeBehavior.php#L56) |

4 subclasses:

- [`BlameableBehavior`](/docs/api/yii/behaviors/blameablebehavior/index.md)
- [`OptimisticLockBehavior`](/docs/api/yii/behaviors/optimisticlockbehavior/index.md)
- [`SluggableBehavior`](/docs/api/yii/behaviors/sluggablebehavior/index.md)
- [`TimestampBehavior`](/docs/api/yii/behaviors/timestampbehavior/index.md)

AttributeBehavior automatically assigns a specified value to one or multiple attributes of an ActiveRecord
object when certain events happen.

To use AttributeBehavior, configure the [`$attributes`](/docs/api/yii/behaviors/attributebehavior/index.md#property-attributes) property which should specify the list of attributes
that need to be updated and the corresponding events that should trigger the update. Then configure the
[`$value`](/docs/api/yii/behaviors/attributebehavior/index.md#property-value) property with a PHP callable whose return value will be used to assign to the current attribute(s).
For example,

```
use yii\behaviors\AttributeBehavior;

public function behaviors()
{
    return [
        [
            'class' => AttributeBehavior::class,
            'attributes' => [
                ActiveRecord::EVENT_BEFORE_INSERT => 'attribute1',
                ActiveRecord::EVENT_BEFORE_UPDATE => 'attribute2',
            ],
            'value' => function ($event) {
                return 'some value';
            },
        ],
    ];
}
```

Because attribute values will be set automatically by this behavior, they are usually not user input and should therefore
not be validated, i.e. they should not appear in the [rules()](/docs/api/yii/base/model/index.md#method-rules) method of the model.

## Properties

| Property | Type | Description | Defined by |
| --- | --- | --- | --- |
| [`$attributes`](#property-attributes) | `array` | List of attributes that are to be automatically filled with the value specified via [`$value`](/docs/api/yii/behaviors/attributebehavior/index.md#property-value). Default: `[]`. | `AttributeBehavior` |
| <span id="property-owner"></span>[`$owner`](/docs/api/yii/base/behavior/index.md#property-owner) | `yii\base\T\|null` | The owner of this behavior Default: `null`. | [`yii\base\Behavior`](/docs/api/yii/base/behavior/index.md) |
| <span id="property-preserveNonEmptyValues"></span>`$preserveNonEmptyValues` | `bool` | Whether to preserve non-empty attribute values. Default: `false`. Available since 2.0.13. | `AttributeBehavior` |
| <span id="property-skipUpdateOnClean"></span>`$skipUpdateOnClean` | `bool` | Whether to skip this behavior when the `$owner` has not been modified Default: `true`. Available since 2.0.8. | `AttributeBehavior` |
| [`$value`](#property-value) | `mixed` | The value that will be assigned to the current attributes. Default: `null`. | `AttributeBehavior` |

## Methods

| Method | Description | Defined by |
| --- | --- | --- |
| <span id="method-__construct"></span>[`__construct()`](/docs/api/yii/base/baseobject/index.md#method-__construct) | Constructor. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__call"></span>[`__call()`](/docs/api/yii/base/baseobject/index.md#method-__call) | Calls the named method which is not a class method. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__get"></span>[`__get()`](/docs/api/yii/base/baseobject/index.md#method-__get) | Returns the value of an object property. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__isset"></span>[`__isset()`](/docs/api/yii/base/baseobject/index.md#method-__isset) | Checks if a property is set, i.e. defined and not null. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__set"></span>[`__set()`](/docs/api/yii/base/baseobject/index.md#method-__set) | Sets value of an object property. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-__unset"></span>[`__unset()`](/docs/api/yii/base/baseobject/index.md#method-__unset) | Sets an object property to null. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-attach"></span>[`attach()`](/docs/api/yii/base/behavior/index.md#method-attach) | Attaches the behavior object to the component. | [`yii\base\Behavior`](/docs/api/yii/base/behavior/index.md) |
| <span id="method-canGetProperty"></span>[`canGetProperty()`](/docs/api/yii/base/baseobject/index.md#method-canGetProperty) | Returns a value indicating whether a property can be read. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-canSetProperty"></span>[`canSetProperty()`](/docs/api/yii/base/baseobject/index.md#method-canSetProperty) | Returns a value indicating whether a property can be set. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-className"></span>[`className()`](/docs/api/yii/base/baseobject/index.md#method-className) static | Returns the fully qualified name of this class. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-detach"></span>[`detach()`](/docs/api/yii/base/behavior/index.md#method-detach) | Detaches the behavior object from the component. | [`yii\base\Behavior`](/docs/api/yii/base/behavior/index.md) |
| [`evaluateAttributes()`](#method-evaluateAttributes) | Evaluates the attribute value and assigns it to the current attributes. | `AttributeBehavior` |
| [`events()`](#method-events) | Declares event handlers for the [`$owner`](/docs/api/yii/base/behavior/index.md#property-owner)'s events. | `AttributeBehavior` |
| <span id="method-hasMethod"></span>[`hasMethod()`](/docs/api/yii/base/baseobject/index.md#method-hasMethod) | Returns a value indicating whether a method is defined. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-hasProperty"></span>[`hasProperty()`](/docs/api/yii/base/baseobject/index.md#method-hasProperty) | Returns a value indicating whether a property is defined. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| <span id="method-init"></span>[`init()`](/docs/api/yii/base/baseobject/index.md#method-init) | Initializes the object. | [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| [`getValue()`](#method-getValue) protected | Returns the value for the current attributes. | `AttributeBehavior` |

## Property details

### $attributes <span id="property-attributes"></span>

```php
public array $attributes = []
```

List of attributes that are to be automatically filled with the value specified via [`$value`](/docs/api/yii/behaviors/attributebehavior/index.md#property-value).

The array keys are the ActiveRecord events upon which the attributes are to be updated,
and the array values are the corresponding attribute(s) to be updated. You can use a string to represent
a single attribute, or an array to represent a list of attributes. For example,

```
[
    ActiveRecord::EVENT_BEFORE_INSERT => ['attribute1', 'attribute2'],
    ActiveRecord::EVENT_BEFORE_UPDATE => 'attribute2',
]
```

### $value <span id="property-value"></span>

```php
public mixed $value = null
```

The value that will be assigned to the current attributes.

This can be an anonymous function,
callable in array format (e.g. `[$this, 'methodName']`), an [Expression](/docs/api/yii/db/expression/index.md) object representing a DB expression
(e.g. `new Expression('NOW()')`), scalar, string or an arbitrary value. If the former, the return value of the
function will be assigned to the attributes.
The signature of the function should be as follows,

```
function ($event)
{
    // return value will be assigned to the attribute
}
```

## Method details

### evaluateAttributes() <span id="method-evaluateAttributes"></span>

```php
public function evaluateAttributes(yii\base\Event $event): mixed
```

Evaluates the attribute value and assigns it to the current attributes.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$event` | [`yii\base\Event`](/docs/api/yii/base/event/index.md) |  |

**Returns**

`mixed`

### events() <span id="method-events"></span>

```php
public function events(): array
```

Declares event handlers for the [`$owner`](/docs/api/yii/base/behavior/index.md#property-owner)'s events.

Child classes may override this method to declare what PHP callbacks should
be attached to the events of the [`$owner`](/docs/api/yii/base/behavior/index.md#property-owner) component.

The callbacks will be attached to the [`$owner`](/docs/api/yii/base/behavior/index.md#property-owner)'s events when the behavior is
attached to the owner; and they will be detached from the events when
the behavior is detached from the component.

The callbacks can be any of the following:

- method in this behavior: `'handleClick'`, equivalent to `[$this, 'handleClick']`
- object method: `[$object, 'handleClick']`
- static method: `['Page', 'handleClick']`
- anonymous function: `function ($event) { ... }`

The following is an example:

```
[
    Model::EVENT_BEFORE_VALIDATE => 'myBeforeValidate',
    Model::EVENT_AFTER_VALIDATE => 'myAfterValidate',
]
```

**Returns**

`array`: Events (array keys) and the corresponding event handler methods (array values).

### getValue() <span id="method-getValue"></span>

```php
protected function getValue(yii\base\Event $event): mixed
```

Returns the value for the current attributes.

This method is called by [`evaluateAttributes()`](/docs/api/yii/behaviors/attributebehavior/index.md#method-evaluateAttributes). Its return value will be assigned
to the attributes corresponding to the triggering event.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$event` | [`yii\base\Event`](/docs/api/yii/base/event/index.md) | The event that triggers the current attribute updating. |

**Returns**

`mixed`: The attribute value