# DbCache

> DbCache implements a cache application component by storing cached data in a database.

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

| class | `yii\caching\DbCache` |
| --- | --- |
| Extends | [`Cache`](/docs/api/yii/caching/cache/index.md) » [`yii\base\Component`](/docs/api/yii/base/component/index.md) » [`yii\base\BaseObject`](/docs/api/yii/base/baseobject/index.md) |
| Implements | [`CacheInterface`](/docs/api/yii/caching/cacheinterface/index.md), [`yii\base\Configurable`](/docs/api/yii/base/configurable/index.md) |
| Since | 2.0 |
| Source | [`framework/caching/DbCache.php`](https://github.com/yiisoft/yii2/blob/22.0/framework/caching/DbCache.php#L44) |

DbCache implements a cache application component by storing cached data in a database.

By default, DbCache stores session data in a DB table named 'cache'. This table
must be pre-created. The table name can be changed by setting [`$cacheTable`](/docs/api/yii/caching/dbcache/index.md#property-cacheTable).

Please refer to [`Cache`](/docs/api/yii/caching/cache/index.md) for common cache operations that are supported by DbCache.

The following example shows how you can configure the application to use DbCache:

```
'cache' => [
    'class' => 'yii\caching\DbCache',
    // 'db' => 'mydb',
    // 'cacheTable' => 'my_cache',
]
```

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-behaviors"></span>[`$behaviors`](/docs/api/yii/base/component/index.md#property-behaviors) read-only | `array<`[`yii\base\Behavior`](/docs/api/yii/base/behavior/index.md)`<static>>` | List of behaviors attached to this component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| [`$cacheTable`](#property-cacheTable) | `string` | Name of the DB table to store cache content. Default: `'{{%cache}}'`. | `DbCache` |
| [`$db`](#property-db) | [`yii\db\Connection`](/docs/api/yii/db/connection/index.md)`\|array\|string` | The DB connection object or the application component ID of the DB connection. Default: `'db'`. | `DbCache` |
| <span id="property-defaultDuration"></span>[`$defaultDuration`](/docs/api/yii/caching/cache/index.md#property-defaultDuration) | `int` | Default duration in seconds before a cache entry will expire. Default: `0`. Available since 2.0.11. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| [`$gcProbability`](#property-gcProbability) | `int` | The probability (parts per million) that garbage collection (GC) should be performed when storing a piece of data in the cache. Default: `100`. | `DbCache` |
| <span id="property-keyPrefix"></span>[`$keyPrefix`](/docs/api/yii/caching/cache/index.md#property-keyPrefix) | `string` | A string prefixed to every cache key so that it is unique globally in the whole cache storage. Default: `null`. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="property-serializer"></span>[`$serializer`](/docs/api/yii/caching/cache/index.md#property-serializer) | `array\|null\|false` | The functions used to serialize and unserialize cached data. Default: `null`. | [`Cache`](/docs/api/yii/caching/cache/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/component/index.md#method-__call) | Calls the named method which is not a class method. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-__clone"></span>[`__clone()`](/docs/api/yii/base/component/index.md#method-__clone) | This method is called after the object is created by cloning an existing one. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-__get"></span>[`__get()`](/docs/api/yii/base/component/index.md#method-__get) | Returns the value of a component property. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-__isset"></span>[`__isset()`](/docs/api/yii/base/component/index.md#method-__isset) | Checks if a property is set, i.e. defined and not null. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-__set"></span>[`__set()`](/docs/api/yii/base/component/index.md#method-__set) | Sets the value of a component property. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-__unset"></span>[`__unset()`](/docs/api/yii/base/component/index.md#method-__unset) | Sets a component property to be null. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-add"></span>[`add()`](/docs/api/yii/caching/cache/index.md#method-add) | Stores a value identified by a key into cache if the cache does not contain this key. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-attachBehavior"></span>[`attachBehavior()`](/docs/api/yii/base/component/index.md#method-attachBehavior) | Attaches a behavior to this component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-attachBehaviors"></span>[`attachBehaviors()`](/docs/api/yii/base/component/index.md#method-attachBehaviors) | Attaches a list of behaviors to the component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-behaviors"></span>[`behaviors()`](/docs/api/yii/base/component/index.md#method-behaviors) | Returns a list of behaviors that this component should behave as. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-buildKey"></span>[`buildKey()`](/docs/api/yii/caching/cache/index.md#method-buildKey) | Builds a normalized cache key from a given key. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-canGetProperty"></span>[`canGetProperty()`](/docs/api/yii/base/component/index.md#method-canGetProperty) | Returns a value indicating whether a property can be read. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-canSetProperty"></span>[`canSetProperty()`](/docs/api/yii/base/component/index.md#method-canSetProperty) | Returns a value indicating whether a property can be set. | [`yii\base\Component`](/docs/api/yii/base/component/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-delete"></span>[`delete()`](/docs/api/yii/caching/cache/index.md#method-delete) | Deletes a value with the specified key from cache. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-detachBehavior"></span>[`detachBehavior()`](/docs/api/yii/base/component/index.md#method-detachBehavior) | Detaches a behavior from the component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-detachBehaviors"></span>[`detachBehaviors()`](/docs/api/yii/base/component/index.md#method-detachBehaviors) | Detaches all behaviors from the component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-ensureBehaviors"></span>[`ensureBehaviors()`](/docs/api/yii/base/component/index.md#method-ensureBehaviors) | Makes sure that the behaviors declared in [`behaviors()`](/docs/api/yii/base/component/index.md#method-behaviors) are attached to this component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| [`exists()`](#method-exists) | Checks whether a specified key exists in the cache. | `DbCache` |
| <span id="method-flush"></span>[`flush()`](/docs/api/yii/caching/cache/index.md#method-flush) | Deletes all values from cache. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| [`gc()`](#method-gc) | Removes the expired data values. | `DbCache` |
| <span id="method-get"></span>[`get()`](/docs/api/yii/caching/cache/index.md#method-get) | Retrieves a value from cache with a specified key. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-getBehavior"></span>[`getBehavior()`](/docs/api/yii/base/component/index.md#method-getBehavior) | Returns the named behavior object. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-getBehaviors"></span>[`getBehaviors()`](/docs/api/yii/base/component/index.md#method-getBehaviors) | Returns all behaviors attached to this component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-getOrSet"></span>[`getOrSet()`](/docs/api/yii/caching/cache/index.md#method-getOrSet) | Method combines both [`set()`](/docs/api/yii/caching/cache/index.md#method-set) and [`get()`](/docs/api/yii/caching/cache/index.md#method-get) methods to retrieve value identified by a $key, or to store the result of $callable execution if there is no cache available for the $key. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-hasEventHandlers"></span>[`hasEventHandlers()`](/docs/api/yii/base/component/index.md#method-hasEventHandlers) | Returns a value indicating whether there is any handler attached to the named event. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-hasMethod"></span>[`hasMethod()`](/docs/api/yii/base/component/index.md#method-hasMethod) | Returns a value indicating whether a method is defined. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-hasProperty"></span>[`hasProperty()`](/docs/api/yii/base/component/index.md#method-hasProperty) | Returns a value indicating whether a property is defined for this component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| [`init()`](#method-init) | Initializes the DbCache component. | `DbCache` |
| <span id="method-multiAdd"></span>[`multiAdd()`](/docs/api/yii/caching/cache/index.md#method-multiAdd) | Stores multiple items in cache. Each item contains a value identified by a key. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-multiGet"></span>[`multiGet()`](/docs/api/yii/caching/cache/index.md#method-multiGet) | Retrieves multiple values from cache with the specified keys. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-multiSet"></span>[`multiSet()`](/docs/api/yii/caching/cache/index.md#method-multiSet) | Stores multiple items in cache. Each item contains a value identified by a key. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-off"></span>[`off()`](/docs/api/yii/base/component/index.md#method-off) | Detaches an existing event handler from this component. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-offsetExists"></span>[`offsetExists()`](/docs/api/yii/caching/cache/index.md#method-offsetExists) | Returns whether there is a cache entry with a specified key. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-offsetGet"></span>[`offsetGet()`](/docs/api/yii/caching/cache/index.md#method-offsetGet) | Retrieves the value from cache with a specified key. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-offsetSet"></span>[`offsetSet()`](/docs/api/yii/caching/cache/index.md#method-offsetSet) | Stores the value identified by a key into cache. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-offsetUnset"></span>[`offsetUnset()`](/docs/api/yii/caching/cache/index.md#method-offsetUnset) | Deletes the value with the specified key from cache This method is required by the interface [`ArrayAccess`](https://www.php.net/manual/en/class.arrayaccess.php). | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-on"></span>[`on()`](/docs/api/yii/base/component/index.md#method-on) | Attaches an event handler to an event. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| <span id="method-set"></span>[`set()`](/docs/api/yii/caching/cache/index.md#method-set) | Stores a value identified by a key into cache. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| <span id="method-trigger"></span>[`trigger()`](/docs/api/yii/base/component/index.md#method-trigger) | Triggers an event. | [`yii\base\Component`](/docs/api/yii/base/component/index.md) |
| [`addValue()`](#method-addValue) protected | Stores a value identified by a key into cache if the cache does not contain this key. | `DbCache` |
| <span id="method-addValues"></span>[`addValues()`](/docs/api/yii/caching/cache/index.md#method-addValues) protected | Adds multiple key-value pairs to cache. | [`Cache`](/docs/api/yii/caching/cache/index.md) |
| [`deleteValue()`](#method-deleteValue) protected | Deletes a value with the specified key from cache This is the implementation of the method declared in the parent class. | `DbCache` |
| [`flushValues()`](#method-flushValues) protected | Deletes all values from cache. | `DbCache` |
| [`getDataFieldName()`](#method-getDataFieldName) protected | Returns the name of the `data` column read by [`getValue()`](/docs/api/yii/caching/dbcache/index.md#method-getValue) and [`getValues()`](/docs/api/yii/caching/dbcache/index.md#method-getValues). | `DbCache` |
| [`getDataFieldValue()`](#method-getDataFieldValue) protected |  | `DbCache` |
| [`getValue()`](#method-getValue) protected | Retrieves a value from cache with a specified key. | `DbCache` |
| [`getValues()`](#method-getValues) protected | Retrieves multiple values from cache with the specified keys. | `DbCache` |
| [`setValue()`](#method-setValue) protected | Stores a value identified by a key in cache. | `DbCache` |
| <span id="method-setValues"></span>[`setValues()`](/docs/api/yii/caching/cache/index.md#method-setValues) protected | Stores multiple key-value pairs in cache. | [`Cache`](/docs/api/yii/caching/cache/index.md) |

## Property details

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

```php
public string $cacheTable = '{{%cache}}'
```

Name of the DB table to store cache content.

The table should be pre-created as follows:

```
CREATE TABLE cache (
    id char(128) NOT NULL PRIMARY KEY,
    expire int(11),
    data BLOB
);
```

For MSSQL:
```
CREATE TABLE cache (
    id VARCHAR(128) NOT NULL PRIMARY KEY,
    expire INT(11),
    data VARBINARY(MAX)
);
```

where 'BLOB' refers to the BLOB-type of your preferred DBMS. Below are the BLOB type
that can be used for some popular DBMS:

- MySQL: LONGBLOB
- PostgreSQL: BYTEA

When using DbCache in a production server, we recommend you create a DB index for the 'expire'
column in the cache table to improve the performance.

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

```php
public yii\db\Connection|array|string $db = 'db'
```

The DB connection object or the application component ID of the DB connection.

After the DbCache object is created, if you want to change this property, you should only assign it
with a DB connection object.
Starting from version 2.0.2, this can also be a configuration array for creating the object.

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

```php
public int $gcProbability = 100
```

The probability (parts per million) that garbage collection (GC) should be performed when storing a piece of data in the cache.

Defaults to 100, meaning 0.01% chance.
This number should be between 0 and 1000000. A value 0 meaning no GC will be performed at all.

## Method details

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

```php
public function exists(mixed $key): bool
```

Checks whether a specified key exists in the cache.

This can be faster than getting the value from the cache if the data is big.
Note that this method does not check whether the dependency associated
with the cached data, if there is any, has changed. So a call to [`get()`](/docs/api/yii/caching/cache/index.md#method-get)
may return false while exists returns true.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$key` | `mixed` | A key identifying the cached value. This can be a simple string or a complex data structure consisting of factors representing the key. |

**Returns**

`bool`: True if a value exists in cache, false if the value is not in the cache or expired.

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

```php
public function gc(bool $force = false): mixed
```

Removes the expired data values.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$force` | `bool` | Whether to enforce the garbage collection regardless of [`$gcProbability`](/docs/api/yii/caching/dbcache/index.md#property-gcProbability). Defaults to false, meaning the actual deletion happens with the probability as specified by [`$gcProbability`](/docs/api/yii/caching/dbcache/index.md#property-gcProbability). |

**Returns**

`mixed`

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

```php
public function init(): mixed
```

Initializes the DbCache component.

This method will initialize the [`$db`](/docs/api/yii/caching/dbcache/index.md#property-db) property to make sure it refers to a valid DB connection.

**Returns**

`mixed`

**Throws**

- [`yii\base\InvalidConfigException`](/docs/api/yii/base/invalidconfigexception/index.md): if [`$db`](/docs/api/yii/caching/dbcache/index.md#property-db) is invalid.

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

```php
protected function addValue(string $key, string $value, int $duration): bool
```

Stores a value identified by a key into cache if the cache does not contain this key.

This is the implementation of the method declared in the parent class.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$key` | `string` | The key identifying the value to be cached |
| `$value` | `string` | The value to be cached. Other types (if you have disabled [`$serializer`](/docs/api/yii/caching/cache/index.md#property-serializer)) cannot be saved. |
| `$duration` | `int` | The number of seconds in which the cached value will expire. 0 means never expire. |

**Returns**

`bool`: True if the value is successfully stored into cache, false otherwise

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

```php
protected function deleteValue(string $key): bool
```

Deletes a value with the specified key from cache
This is the implementation of the method declared in the parent class.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$key` | `string` | The key of the value to be deleted |

**Returns**

`bool`: If no error happens during deletion

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

```php
protected function flushValues(): bool
```

Deletes all values from cache.

This is the implementation of the method declared in the parent class.

**Returns**

`bool`: Whether the flush operation was successful.

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

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

Returns the name of the `data` column read by [`getValue()`](/docs/api/yii/caching/dbcache/index.md#method-getValue) and [`getValues()`](/docs/api/yii/caching/dbcache/index.md#method-getValues).

Override to wrap the column in a database expression aliased as `data`.

**Returns**

`string`: Column name or expression aliased as `data`.

**Since**

2.0.42

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

```php
protected function getDataFieldValue(mixed $value): mixed
```

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$value` | `mixed` |  |

**Returns**

`mixed`: Value prepared by the `data` column schema.

**Since**

2.0.42

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

```php
protected function getValue(string $key): string|false
```

Retrieves a value from cache with a specified key.

This is the implementation of the method declared in the parent class.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$key` | `string` | A unique key identifying the cached value |

**Returns**

`string|false`: The value stored in cache, false if the value is not in the cache or expired.

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

```php
protected function getValues(array $keys): array
```

Retrieves multiple values from cache with the specified keys.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$keys` | `array` | A list of keys identifying the cached values. |

**Returns**

`array`: A list of cached values indexed by the keys.

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

```php
protected function setValue(string $key, string $value, int $duration): bool
```

Stores a value identified by a key in cache.

This is the implementation of the method declared in the parent class.

**Parameters**

| Parameter | Type | Description |
| --- | --- | --- |
| `$key` | `string` | The key identifying the value to be cached |
| `$value` | `string` | The value to be cached. Other types (if you have disabled [`$serializer`](/docs/api/yii/caching/cache/index.md#property-serializer)) cannot be saved. |
| `$duration` | `int` | The number of seconds in which the cached value will expire. 0 means never expire. |

**Returns**

`bool`: True if the value is successfully stored into cache, false otherwise