# Dependency

> Dependency is the base class for cache dependency classes.

[API reference](/docs/api/index.md) › [yii](/docs/api/yii/index.md) › [caching](/docs/api/yii/caching/index.md) › Dependency

| abstract class | `yii\caching\Dependency` |
| --- | --- |
| Extends | [`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/caching/Dependency.php`](https://github.com/yiisoft/yii2/blob/22.0/framework/caching/Dependency.php#L22) |

7 subclasses:

- [`CallbackDependency`](/docs/api/yii/caching/callbackdependency/index.md)
- [`ChainedDependency`](/docs/api/yii/caching/chaineddependency/index.md)
- [`DbDependency`](/docs/api/yii/caching/dbdependency/index.md)
- [`DbQueryDependency`](/docs/api/yii/caching/dbquerydependency/index.md)
- [`ExpressionDependency`](/docs/api/yii/caching/expressiondependency/index.md)
- [`FileDependency`](/docs/api/yii/caching/filedependency/index.md)
- [`TagDependency`](/docs/api/yii/caching/tagdependency/index.md)

Dependency is the base class for cache dependency classes.

Child classes should override its [`generateDependencyData()`](/docs/api/yii/caching/dependency/index.md#method-generateDependencyData) for generating
the actual dependency data.

For more details and usage information on Cache, see the [guide article on caching](/docs/guide/caching-overview/index.md).

## Properties

| Property | Type | Description | Defined by |
| --- | --- | --- | --- |
| <span id="property-data"></span>`$data` | `mixed` | The dependency data that is saved in cache and later is compared with the latest dependency data. Default: `null`. | `Dependency` |
| [`$reusable`](#property-reusable) | `bool` | Whether this dependency is reusable or not. Default: `false`. | `Dependency` |

## 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-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) |
| [`evaluateDependency()`](#method-evaluateDependency) | Evaluates the dependency by generating and saving the data related with dependency. | `Dependency` |
| <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) |
| [`isChanged()`](#method-isChanged) | Checks whether the dependency is changed. | `Dependency` |
| [`resetReusableData()`](#method-resetReusableData) static | Resets all cached data for reusable dependencies. | `Dependency` |
| [`generateDependencyData()`](#method-generateDependencyData) protected abstract | Generates the data needed to determine if dependency is changed. | `Dependency` |
| [`generateReusableHash()`](#method-generateReusableHash) protected | Generates a unique hash that can be used for retrieving reusable dependency data. | `Dependency` |

## Property details

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

```php
public bool $reusable = false
```

Whether this dependency is reusable or not.

True value means that dependent
data for this cache dependency will be generated only once per request. This allows you
to use the same cache dependency for multiple separate cache calls while generating the same
page without an overhead of re-evaluating dependency data each time. Defaults to false.

## Method details

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

```php
public function evaluateDependency(yii\caching\CacheInterface $cache): mixed
```

Evaluates the dependency by generating and saving the data related with dependency.

This method is invoked by cache before writing data into it.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$cache` | [`CacheInterface`](/docs/api/yii/caching/cacheinterface/index.md) | The cache component that is currently evaluating this dependency |

**Returns**

`mixed`

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

```php
public function isChanged(yii\caching\CacheInterface $cache): bool
```

Checks whether the dependency is changed.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$cache` | [`CacheInterface`](/docs/api/yii/caching/cacheinterface/index.md) | The cache component that is currently evaluating this dependency |

**Returns**

`bool`: Whether the dependency has changed.

**Since**

2.0.11

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

```php
public static function resetReusableData(): mixed
```

Resets all cached data for reusable dependencies.

**Returns**

`mixed`

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

```php
abstract protected function generateDependencyData(yii\caching\CacheInterface $cache): mixed
```

Generates the data needed to determine if dependency is changed.

Derived classes should override this method to generate the actual dependency data.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$cache` | [`CacheInterface`](/docs/api/yii/caching/cacheinterface/index.md) | The cache component that is currently evaluating this dependency |

**Returns**

`mixed`: The data needed to determine if dependency has been changed.

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

```php
protected function generateReusableHash(): string
```

Generates a unique hash that can be used for retrieving reusable dependency data.

**Returns**

`string`: A unique hash value for this cache dependency.

**See also**

- [`$reusable`](/docs/api/yii/caching/dependency/index.md#property-reusable)