# Class yii\caching\DbDependency

Inheritance | yii\caching\DbDependency » 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/DbDependency.php

DbDependency represents a dependency based on the query result of a SQL statement.

If the query result changes, the dependency is considered as changed. The query is specified via the $sql property.

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
$db | string | The application component ID of the DB connection. | yii\caching\DbDependency
$params | array | The parameters (name => value) to be bound to the SQL statement specified by $sql. | yii\caching\DbDependency
$reusable | boolean | Whether this dependency is reusable or not. | yii\caching\Dependency
$sql | string | The SQL query whose result is used to determine if the dependency has been changed. | yii\caching\DbDependency

## 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\DbDependency
generateReusableHash() | Generates a unique hash that can be used for retrieving reusable dependency data. | yii\caching\Dependency

## Property Details

$db public property

The application component ID of the DB connection.

public string $db = 'db'
$params public property

The parameters (name => value) to be bound to the SQL statement specified by $sql.

public array $params = []
$sql public property

The SQL query whose result is used to determine if the dependency has been changed. Only the first row of the query result will be used.

public string $sql = null

## Method Details

generateDependencyData() protected method

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

This method returns the value of the global state.

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.
throws | yii\base\InvalidConfigException | if $db is not a valid application component ID