# Class yii\caching\DbCache

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

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.

Please refer to yii\caching\Cache 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.

## Public Properties

Hide inherited properties

Property | Type | Description | Defined By
--- | --- | --- | ---
$behaviors | yii\base\Behavior[] | List of behaviors attached to this component. This property is read-only. | yii\base\Component
$cacheTable | string | Name of the DB table to store cache content. | yii\caching\DbCache
$db | yii\db\Connection|array|string | The DB connection object or the application component ID of the DB connection. | yii\caching\DbCache
$defaultDuration | integer | Default duration in seconds before a cache entry will expire. | yii\caching\Cache
$gcProbability | integer | The probability (parts per million) that garbage collection (GC) should be performed when storing a piece of data in the cache. | yii\caching\DbCache
$keyPrefix | string | A string prefixed to every cache key so that it is unique globally in the whole cache storage. | yii\caching\Cache
$serializer | null|array|false | The functions used to serialize and unserialize cached data. | yii\caching\Cache

## Public Methods

Hide inherited methods

Method | Description | Defined By
--- | --- | ---
__call() | Calls the named method which is not a class method. | yii\base\Component
__clone() | This method is called after the object is created by cloning an existing one. | yii\base\Component
__construct() | Constructor. | yii\base\BaseObject
__get() | Returns the value of a component property. | yii\base\Component
__isset() | Checks if a property is set, i.e. defined and not null. | yii\base\Component
__set() | Sets the value of a component property. | yii\base\Component
__unset() | Sets a component property to be null. | yii\base\Component
add() | Stores a value identified by a key into cache if the cache does not contain this key. | yii\caching\Cache
attachBehavior() | Attaches a behavior to this component. | yii\base\Component
attachBehaviors() | Attaches a list of behaviors to the component. | yii\base\Component
behaviors() | Returns a list of behaviors that this component should behave as. | yii\base\Component
buildKey() | Builds a normalized cache key from a given key. | yii\caching\Cache
canGetProperty() | Returns a value indicating whether a property can be read. | yii\base\Component
canSetProperty() | Returns a value indicating whether a property can be set. | yii\base\Component
className() | Returns the fully qualified name of this class. | yii\base\BaseObject
delete() | Deletes a value with the specified key from cache. | yii\caching\Cache
detachBehavior() | Detaches a behavior from the component. | yii\base\Component
detachBehaviors() | Detaches all behaviors from the component. | yii\base\Component
ensureBehaviors() | Makes sure that the behaviors declared in behaviors() are attached to this component. | yii\base\Component
exists() | Checks whether a specified key exists in the cache. | yii\caching\DbCache
flush() | Deletes all values from cache. | yii\caching\Cache
gc() | Removes the expired data values. | yii\caching\DbCache
get() | Retrieves a value from cache with a specified key. | yii\caching\Cache
getBehavior() | Returns the named behavior object. | yii\base\Component
getBehaviors() | Returns all behaviors attached to this component. | yii\base\Component
getOrSet() | Method combines both set() and 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. | yii\caching\Cache
hasEventHandlers() | Returns a value indicating whether there is any handler attached to the named event. | yii\base\Component
hasMethod() | Returns a value indicating whether a method is defined. | yii\base\Component
hasProperty() | Returns a value indicating whether a property is defined for this component. | yii\base\Component
init() | Initializes the DbCache component. | yii\caching\DbCache
madd() | Stores multiple items in cache. Each item contains a value identified by a key. | yii\caching\Cache
mget() | Retrieves multiple values from cache with the specified keys. | yii\caching\Cache
mset() | Stores multiple items in cache. Each item contains a value identified by a key. | yii\caching\Cache
multiAdd() | Stores multiple items in cache. Each item contains a value identified by a key. | yii\caching\Cache
multiGet() | Retrieves multiple values from cache with the specified keys. | yii\caching\Cache
multiSet() | Stores multiple items in cache. Each item contains a value identified by a key. | yii\caching\Cache
off() | Detaches an existing event handler from this component. | yii\base\Component
offsetExists() | Returns whether there is a cache entry with a specified key. | yii\caching\Cache
offsetGet() | Retrieves the value from cache with a specified key. | yii\caching\Cache
offsetSet() | Stores the value identified by a key into cache. | yii\caching\Cache
offsetUnset() | Deletes the value with the specified key from cache This method is required by the interface ArrayAccess. | yii\caching\Cache
on() | Attaches an event handler to an event. | yii\base\Component
set() | Stores a value identified by a key into cache. | yii\caching\Cache
trigger() | Triggers an event. | yii\base\Component

## Protected Methods

Hide inherited methods

Method | Description | Defined By
--- | --- | ---
addValue() | Stores a value identified by a key into cache if the cache does not contain this key. | yii\caching\DbCache
addValues() | Adds multiple key-value pairs to cache. | yii\caching\Cache
deleteValue() | Deletes a value with the specified key from cache This is the implementation of the method declared in the parent class. | yii\caching\DbCache
flushValues() | Deletes all values from cache. | yii\caching\DbCache
getValue() | Retrieves a value from cache with a specified key. | yii\caching\DbCache
getValues() | Retrieves multiple values from cache with the specified keys. | yii\caching\DbCache
setValue() | Stores a value identified by a key in cache. | yii\caching\DbCache
setValues() | Stores multiple key-value pairs in cache. | yii\caching\Cache

## Property Details

$cacheTable public property

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
    );

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
- MSSQL: BLOB

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.

public string $cacheTable = '{{%cache}}'
$db public property

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.

public yii\db\Connection|array|string $db = 'db'
$gcProbability public property

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.

public integer $gcProbability = 100

## Method Details

addValue() protected method

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.

protected boolean addValue ( $key, $value, $duration )
$key | string | The key identifying the value to be cached
$value | string | The value to be cached. Other types (if you have disabled $serializer) cannot be saved.
$duration | integer | The number of seconds in which the cached value will expire. 0 means never expire.
return | boolean | True if the value is successfully stored into cache, false otherwise

deleteValue() protected method

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

protected boolean deleteValue ( $key )
$key | string | The key of the value to be deleted
return | boolean | If no error happens during deletion

exists() public method

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() may return false while exists returns true.

public boolean exists ( $key )
$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.
return | boolean | True if a value exists in cache, false if the value is not in the cache or expired.

flushValues() protected method

Deletes all values from cache.

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

protected boolean flushValues ( )
return | boolean | Whether the flush operation was successful.

gc() public method

Removes the expired data values.

public void gc ( $force = false )
$force | boolean | Whether to enforce the garbage collection regardless of $gcProbability. Defaults to false, meaning the actual deletion happens with the probability as specified by $gcProbability.

getValue() protected method

Retrieves a value from cache with a specified key.

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

protected string|false getValue ( $key )
$key | string | A unique key identifying the cached value
return | string|false | The value stored in cache, false if the value is not in the cache or expired.

getValues() protected method

Retrieves multiple values from cache with the specified keys.

protected array getValues ( $keys )
$keys | array | A list of keys identifying the cached values
return | array | A list of cached values indexed by the keys

init() public method

Initializes the DbCache component.

This method will initialize the $db property to make sure it refers to a valid DB connection.

public void init ( )
throws | yii\base\InvalidConfigException | if $db is invalid.

setValue() protected method

Stores a value identified by a key in cache.

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

protected boolean setValue ( $key, $value, $duration )
$key | string | The key identifying the value to be cached
$value | string | The value to be cached. Other types (if you have disabled $serializer) cannot be saved.
$duration | integer | The number of seconds in which the cached value will expire. 0 means never expire.
return | boolean | True if the value is successfully stored into cache, false otherwise