# Class yii\caching\ExpressionDependency

Inheritance | yii\caching\ExpressionDependency » yii\caching\Dependency » yii\base\BaseObject
Implements | yii\base\Configurable
Available since version | 2.0
Source Code | https://github.com/yiisoft/yii2/blob/master/framework/caching/ExpressionDependency.php

ExpressionDependency represents a dependency based on the result of a PHP expression.

ExpressionDependency will use `eval()` to evaluate the PHP expression. The dependency is reported as unchanged if and only if the result of the expression is the same as the one evaluated when storing the data to cache.

A PHP expression can be any PHP code that has a value. To learn more about what an expression is, please refer to the php manual.

For more details and usage information on Cache, see the guide article on caching.

## Public Properties

Hide inherited properties

Property | Type | Description | Defined By
--- | --- | --- | ---
$data | mixed | The dependency data that is saved in cache and later is compared with the latest dependency data. | yii\caching\Dependency
$expression | string | The string representation of a PHP expression whose result is used to determine the dependency. | yii\caching\ExpressionDependency
$params | mixed | Custom parameters associated with this dependency. | yii\caching\ExpressionDependency
$reusable | boolean | Whether this dependency is reusable or not. | yii\caching\Dependency

## Public Methods

Hide inherited methods

Method | Description | Defined By
--- | --- | ---
__call() | Calls the named method which is not a class method. | yii\base\BaseObject
__construct() | Constructor. | yii\base\BaseObject
__get() | Returns the value of an object property. | yii\base\BaseObject
__isset() | Checks if a property is set, i.e. defined and not null. | yii\base\BaseObject
__set() | Sets value of an object property. | yii\base\BaseObject
__unset() | Sets an object property to null. | yii\base\BaseObject
canGetProperty() | Returns a value indicating whether a property can be read. | yii\base\BaseObject
canSetProperty() | Returns a value indicating whether a property can be set. | yii\base\BaseObject
className() | Returns the fully qualified name of this class. | yii\base\BaseObject
evaluateDependency() | Evaluates the dependency by generating and saving the data related with dependency. | yii\caching\Dependency
getHasChanged() | Returns a value indicating whether the dependency has changed. | yii\caching\Dependency
hasMethod() | Returns a value indicating whether a method is defined. | yii\base\BaseObject
hasProperty() | Returns a value indicating whether a property is defined. | yii\base\BaseObject
init() | Initializes the object. | yii\base\BaseObject
isChanged() | Checks whether the dependency is changed. | yii\caching\Dependency
resetReusableData() | Resets all cached data for reusable dependencies. | yii\caching\Dependency

## Protected Methods

Hide inherited methods

Method | Description | Defined By
--- | --- | ---
generateDependencyData() | Generates the data needed to determine if dependency has been changed. | yii\caching\ExpressionDependency
generateReusableHash() | Generates a unique hash that can be used for retrieving reusable dependency data. | yii\caching\Dependency

## Property Details

$expression public property

The string representation of a PHP expression whose result is used to determine the dependency. A PHP expression can be any PHP code that evaluates to a value. To learn more about what an expression is, please refer to the php manual.

public string $expression = 'true'
$params public property

Custom parameters associated with this dependency. You may get the value of this property in $expression using `$this->params`.

public mixed $params = null

## Method Details

generateDependencyData() protected method

Generates the data needed to determine if dependency has been changed.

This method returns the result of the PHP expression.

protected mixed generateDependencyData ( $cache )
$cache | yii\caching\CacheInterface | The cache component that is currently evaluating this dependency
return | mixed | The data needed to determine if dependency has been changed.