# DbQueryDependency

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

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

| class | `yii\caching\DbQueryDependency` |
| --- | --- |
| Extends | [`Dependency`](/docs/api/yii/caching/dependency/index.md) » [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| Implements | [`yii\base\Configurable`](/docs/api/yii/base/configurable/index.md) |
| Since | 2.0.12 |
| Source | [`framework/caching/DbQueryDependency.php`](https://github.com/yiisoft/yii2/blob/22.0/framework/caching/DbQueryDependency.php#L31) |

DbQueryDependency represents a dependency based on the query result of an [`QueryInterface`](/docs/api/yii/db/queryinterface/index.md) instance.

If the query result changes, the dependency is considered as changed.
The query is specified via the [`$query`](/docs/api/yii/caching/dbquerydependency/index.md#property-query) property.

Object of any class which matches [`QueryInterface`](/docs/api/yii/db/queryinterface/index.md) 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](/docs/guide/caching-overview/index.md).

See also: [`QueryInterface`](/docs/api/yii/db/queryinterface/index.md).

## Properties

| Property | Type | Description | Defined by |
| --- | --- | --- | --- |
| <span id="property-data"></span>[`$data`](/docs/api/yii/caching/dependency/index.md#property-data) | `mixed` | The dependency data that is saved in cache and later is compared with the latest dependency data. Default: `null`. | [`Dependency`](/docs/api/yii/caching/dependency/index.md) |
| [`$db`](#property-db) | `string\|array\|object` | The application component ID of the database connection, connection object or its array configuration. Default: `null`. | `DbQueryDependency` |
| [`$method`](#property-method) | `string\|callable\|null` | Method which should be invoked in over the [`$query`](/docs/api/yii/caching/dbquerydependency/index.md#property-query) object. Default: `null`. | `DbQueryDependency` |
| [`$query`](#property-query) | [`yii\db\QueryInterface`](/docs/api/yii/db/queryinterface/index.md) | The query which result is used to determine if the dependency has been changed. Default: `null`. | `DbQueryDependency` |
| <span id="property-reusable"></span>[`$reusable`](/docs/api/yii/caching/dependency/index.md#property-reusable) | `bool` | Whether this dependency is reusable or not. Default: `false`. | [`Dependency`](/docs/api/yii/caching/dependency/index.md) |

## 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) |
| <span id="method-evaluateDependency"></span>[`evaluateDependency()`](/docs/api/yii/caching/dependency/index.md#method-evaluateDependency) | Evaluates the dependency by generating and saving the data related with dependency. | [`Dependency`](/docs/api/yii/caching/dependency/index.md) |
| <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) |
| <span id="method-isChanged"></span>[`isChanged()`](/docs/api/yii/caching/dependency/index.md#method-isChanged) | Checks whether the dependency is changed. | [`Dependency`](/docs/api/yii/caching/dependency/index.md) |
| <span id="method-resetReusableData"></span>[`resetReusableData()`](/docs/api/yii/caching/dependency/index.md#method-resetReusableData) static | Resets all cached data for reusable dependencies. | [`Dependency`](/docs/api/yii/caching/dependency/index.md) |
| [`generateDependencyData()`](#method-generateDependencyData) protected | Generates the data needed to determine if dependency is changed. | `DbQueryDependency` |
| <span id="method-generateReusableHash"></span>[`generateReusableHash()`](/docs/api/yii/caching/dependency/index.md#method-generateReusableHash) protected | Generates a unique hash that can be used for retrieving reusable dependency data. | [`Dependency`](/docs/api/yii/caching/dependency/index.md) |

## Property details

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

```php
public string|array|object $db = null
```

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.

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

```php
public string|callable|null $method = null
```

Method which should be invoked in over the [`$query`](/docs/api/yii/caching/dbquerydependency/index.md#property-query) object.

If specified as a string an own query method with such name will be invoked, passing [`$db`](/docs/api/yii/caching/dbquerydependency/index.md#property-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 - [`QueryInterface::one()`](/docs/api/yii/db/queryinterface/index.md#method-one) will be used.

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

```php
public yii\db\QueryInterface $query = null
```

The query which result is used to determine if the dependency has been changed.

Actual query method to be invoked is determined by [`$method`](/docs/api/yii/caching/dbquerydependency/index.md#property-method).

## Method details

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

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

Generates the data needed to determine if dependency is changed.

This method returns the query result.

**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.

**Throws**

- [`yii\base\InvalidConfigException`](/docs/api/yii/base/invalidconfigexception/index.md): on invalid configuration.