Class \Prado\Caching\TDbCache

TDbCache class

TDbCache implements a cache application module by storing cached data in a database.

TDbCache relies on PDO to retrieve data from databases. In order to use TDbCache, you need to enable the PDO extension as well as the corresponding PDO DB driver. For example, to use SQLite database to store cached data, you need both php_pdo and php_pdo_sqlite extensions.

By default, TDbCache creates and uses an SQLite database under the application runtime directory. You may change this default setting by specifying the following properties:

ConnectionID or
ConnectionString, Username and Pasword.

The cached data is stored in a table in the specified database. By default, the name of the table is called 'pradocache'. If the table does not exist in the database, it will be automatically created with the following structure:

CREATE TABLE pradocache (itemkey CHAR(128), value BLOB, expire INT)
CREATE INDEX IX_itemkey ON pradocache (itemkey)
CREATE INDEX IX_expire ON pradocache (expire)

Note, some DBMS might not support BLOB type. In this case, replace 'BLOB' with a suitable binary data type (e.g. LONGBLOB in MySQL, BYTEA in PostgreSQL.)

Important: Make sure that the indices are non-unique!

If you want to change the cache table name, or if you want to create the table by yourself, you may set CacheTableName and AutoCreateCacheTableName properties.

FlushInterval control how often expired items will be removed from cache. If you prefer to remove expired items manualy e.g. via cronjob you can disable automatic deletion by setting FlushInterval to '0'.

The following basic cache operations are implemented:

self::get() : retrieve the value with a key (if any) from cache
TDbCache::set() : store the value with a key into cache
TDbCache::add() : store the value only if cache does not have this key
TDbCache::delete() : delete the value with the specified key from cache
TDbCache::flush() : delete all values from cache

Each value is associated with an expiration time. The TDbCache::get() operation ensures that any expired value will not be returned. The expiration time by the number of seconds. A expiration time 0 represents never expire.

By definition, cache does not ensure the existence of a value even if it never expires. Cache is not meant to be an persistent storage.

Do not use the same database file for multiple applications using TDbCache. Also note, cache is shared by all user sessions of an application.

Some usage examples of TDbCache are as follows,

$cache=new TDbCache;  // TDbCache may also be loaded as a Prado application module
$cache->init(null);
$cache->add('object',$object);
$object2=$cache->get('object');

If loaded, TDbCache will register itself with TApplication as the cache module. It can be accessed via TApplication::getCache().

TDbCache may be configured in application configuration file as follows

<module id="cache" class="Prado\Caching\TDbCache" />

Class hierarchy

\Prado\Caching\TDbCache implements IDbModule

\Prado\Caching\TCache implements ICache, ArrayAccess

\Prado\TModule implements IModule

\Prado\TApplicationComponent

\Prado\TComponent

Author: Qiang Xue <qiang.xue@gmail.com>
Since: 3.1.0

Methods summary
`public`	`__destruct() : mixed` Destructor. Disconnect the db connection.
`public`	`doFlushCacheExpired() : mixed` Event listener for TApplication.OnSaveState
`public`	`doInitializeCache() : mixed` Event listener for TApplication.OnLoadStateComplete
`public`	`flush() : bool` Deletes all values from cache. Be careful of performing this operation if the cache is shared by multiple applications.
`public`	`flushCacheExpired([bool $force = false ]) : mixed` Flush expired values from cache depending on {@see \Prado\Caching\TDbCache::setFlushInterval() FlushInterval}
`public`	`fxGetCronTaskInfos(object $sender, mixed $param) : mixed`
`public`	`getAutoCreateCacheTable() : bool`
`public`	`getCacheTableName() : string`
`public`	`getConnectionID() : string`
`public`	`getConnectionString() : string`
`public`	`getDbConnection() : TDbConnection`
`public`	`getFlushInterval() : int`
`public`	`getPassword() : string`
`public`	`getUsername() : string`
`public`	`init(TXmlElement $config) : mixed` Initializes this module. This method is required by the IModule interface. attach TDbCache::doInitializeCache() to TApplication.OnLoadStateComplete event attach TDbCache::doFlushCacheExpired() to TApplication.OnSaveState event
`public`	`setAutoCreateCacheTable(bool $value) : mixed`
`public`	`setCacheTableName(string $value) : mixed` Sets the name of the DB table to store cache content. Note, if AutoCreateCacheTable is false and you want to create the DB table manually by yourself, you need to make sure the DB table is of the following structure: `CREATE TABLE pradocache (itemkey CHAR(128), value BLOB, expire INT) CREATE INDEX IX_itemkey ON pradocache (itemkey) CREATE INDEX IX_expire ON pradocache (expire)` Note, some DBMS might not support BLOB type. In this case, replace 'BLOB' with a suitable binary data type (e.g. LONGBLOB in MySQL, BYTEA in PostgreSQL.) Important: Make sure that the indices are non-unique!
`public`	`setConnectionID(string $value) : mixed` Sets the ID of a TDataSourceConfig module. The datasource module will be used to establish the DB connection for this cache module. The database connection can also be specified via ConnectionString. When both ConnectionID and ConnectionString are specified, the former takes precedence.
`public`	`setConnectionString(string $value) : mixed`
`public`	`setFlushInterval(int $value) : mixed` Sets interval expired items will be removed from cache To disable automatic deletion of expired items, e.g. for external flushing via cron you can set value to '0'
`public`	`setPassword(string $value) : mixed`
`public`	`setUsername(string $value) : mixed`
`protected`	`addValue(string $key, string $value, int $expire) : 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.
`protected`	`createDbConnection() : TDbConnection` Creates the DB connection.
`protected`	`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.
`protected`	`getValue(string $key) : false\|string` Retrieves a value from cache with a specified key. This is the implementation of the method declared in the parent class.
`protected`	`initializeCache([bool $force = false ]) : mixed` Initialize TDbCache If AutoCreateCacheTableName is 'true' check existence of cache table and create table if does not exist.
`protected`	`setValue(string $key, string $value, int $expire) : bool` Stores a value identified by a key in cache. This is the implementation of the method declared in the parent class.

Inherited methods
__call, __callStatic, __clone, __construct, __destruct, __get, __isset, __set, __sleep, __unset, __wakeup, add, addParsedObject, asa, attachBehavior, attachBehaviors, attachClassBehavior, attachEventHandler, callBehaviorsMethod, canGetProperty, canSetProperty, clearBehaviors, createdOnTemplate, delete, detachBehavior, detachBehaviors, detachClassBehavior, detachEventHandler, disableBehavior, disableBehaviors, enableBehavior, enableBehaviors, evaluateExpression, evaluateStatements, flush, fxAttachClassBehavior, fxDetachClassBehavior, get, getApplication, getAutoGlobalListen, getBehaviors, getBehaviorsEnabled, getClassHierarchy, getEventHandlers, getID, getKeyPrefix, getListeningToGlobalEvents, getPrimaryCache, getRequest, getResponse, getService, getSession, getSubProperty, getUser, hasEvent, hasEventHandler, hasMethod, hasProperty, init, isa, listen, offsetExists, offsetGet, offsetSet, offsetUnset, publishAsset, publishFilePath, raiseEvent, set, setID, setKeyPrefix, setPrimaryCache, setSubProperty, unlisten, _getZappableSleepProps, addValue, deleteValue, generateUniqueKey, getCallChain, getClassFxEvents, getValue, instanceBehavior, setValue, filter_prado_fx

Inherited constants
`\Prado\TApplicationComponent::FX_CACHE_FILE, \Prado\TComponent::GLOBAL_RAISE_EVENT_LISTENER`

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Class \Prado\Caching\TDbCache

Class hierarchy