# Class yii\caching\DbQueryDependency

Inheritance | yii\caching\DbQueryDependency » yii\caching\Dependency » yii\base\BaseObject
Implements | yii\base\Configurable
Available since version | 2.0.12
Source Code | https://github.com/yiisoft/yii2/blob/master/framework/caching/DbQueryDependency.php

DbQueryDependency represents a dependency based on the query result of an yii\db\QueryInterface instance.

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

Object of any class which matches yii\db\QueryInterface can be used, so this dependency can be used not only with regular relational databases but with MongoDB, Redis and so on as well.

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

See also yii\db\QueryInterface.

## 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|array|object | The application component ID of the database connection, connection object or its array configuration. | yii\caching\DbQueryDependency
$method | string|callable | Method which should be invoked in over the $query object. | yii\caching\DbQueryDependency
$query | yii\db\QueryInterface | The query which result is used to determine if the dependency has been changed. | yii\caching\DbQueryDependency
$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 is changed. | yii\caching\DbQueryDependency
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 database connection, connection object or its array configuration. This field can be left blank, allowing query to determine connection automatically.

public string|array|object $db = null
$method public property

Method which should be invoked in over the $query object.

If specified as a string an own query method with such name will be invoked, passing $db value as its first argument. For example: `exists`, `all`.

This field can be specified as a PHP callback of following signature:

    function (QueryInterface $query, mixed $db) {
        //return mixed;
    }

If not set - yii\db\QueryInterface::one() will be used.

public string|callable $method = null
$query public property

The query which result is used to determine if the dependency has been changed. Actual query method to be invoked is determined by $method.

public yii\db\QueryInterface $query = null

## Method Details

generateDependencyData() protected method

Generates the data needed to determine if dependency is changed.

This method returns the query result.

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 | on invalid configuration.