## Class TDbCache

Description

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: (itemkey CHAR(128) PRIMARY KEY, value BLOB, expire INT)

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.)

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.

The following basic cache operations are implemented:

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

Each value is associated with an expiration time. The 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="System.Caching.TDbCache" />

- since: 3.1.0
- version: $Id: TDbCache.php 2496 2008-08-14 10:16:47Z knut $
- author: Qiang Xue <qiang.xue@gmail.com>

Located in /Caching/TDbCache.php (line 80)

    TComponent
       |
       --TApplicationComponent
          |
          --TModule
             |
             --TCache
                |
                --TDbCache

Method Summary
void __destruct ()
boolean addValue (string $key, string $value, integer $expire)
TDbConnection createDbConnection (string 0)
boolean deleteValue (string $key)
void flush ()
boolean getAutoCreateCacheTable ()
string getCacheTableName ()
string getConnectionID ()
string getConnectionString ()
TDbConnection getDbConnection ()
string getPassword ()
string getUsername ()
string getValue (string $key)
void init (TXmlElement $config)
void setAutoCreateCacheTable (boolean $value)
void setCacheTableName (string $value)
void setConnectionID (string $value)
void setConnectionString (string $value)
void setPassword (string $value)
void setUsername (string $value)
boolean setValue (string $key, string $value, integer $expire)
Methods
Destructor __destruct (line 106)

Destructor.

Disconnect the db connection.

- access: public

void __destruct ()
addValue (line 352)

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.

- return: true if the value is successfully stored into cache, false otherwise
- access: protected

boolean addValue (string $key, string $value, integer $expire)

- string $key: the key identifying the value to be cached
- string $value: the value to be cached
- integer $expire: the number of seconds in which the cached value will expire. 0 means never expire.

Redefinition of:

TCache::addValue()
  Stores a value identified by a key into cache if the cache does not contain this key.

createDbConnection (line 161)

Creates the DB connection.

- return: the created DB connection
- access: protected
- throws: TConfigurationException if module ID is invalid or empty

TDbConnection createDbConnection (string 0)

- string 0: the module ID for TDataSourceConfig

deleteValue (line 376)

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

- return: if no error happens during deletion
- access: protected

boolean deleteValue (string $key)

- string $key: the key of the value to be deleted

Redefinition of:

TCache::deleteValue()
  Deletes a value with the specified key from cache This method should be implemented by child classes to delete the data from actual cache storage.

flush (line 388)

Deletes all values from cache.

Be careful of performing this operation if the cache is shared by multiple applications.

- access: public

void flush ()

Redefinition of:

TCache::flush()
  Deletes all values from cache.

getAutoCreateCacheTable (line 302)

- return: whether the cache DB table should be automatically created if not exists. Defaults to true.
- access: public
- see: TDbCache::setAutoCreateCacheTable()

boolean getAutoCreateCacheTable ()
getCacheTableName (line 277)

- return: the name of the DB table to store cache content. Defaults to 'pradocache'.
- access: public
- see: TDbCache::setAutoCreateCacheTable()

string getCacheTableName ()
getConnectionID (line 206)

- return: the ID of a TDataSourceConfig module. Defaults to empty string, meaning not set.
- access: public
- since: 3.1.1

string getConnectionID ()
getConnectionString (line 227)

- return: The Data Source Name, or DSN, contains the information required to connect to the database.
- access: public

string getConnectionString ()
getDbConnection (line 195)

- return: the DB connection instance
- access: public

TDbConnection getDbConnection ()
getPassword (line 260)

- return: the password for establishing DB connection. Defaults to empty string.
- access: public

string getPassword ()
getUsername (line 244)

- return: the username for establishing DB connection. Defaults to empty string.
- access: public

string getUsername ()
getValue (line 322)

Retrieves a value from cache with a specified key.

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

- return: the value stored in cache, false if the value is not in the cache or expired.
- access: protected

string getValue (string $key)

- string $key: a unique key identifying the cached value

Redefinition of:

TCache::getValue()
  Retrieves a value from cache with a specified key.

init (line 122)

Initializes this module.

This method is required by the IModule interface. It checks if the DbFile property is set, and creates a SQLiteDatabase instance for it. The database or the cache table does not exist, they will be created. Expired values are also deleted.

- access: public
- throws: TConfigurationException if sqlite extension is not installed, DbFile is set invalid, or any error happens during creating database or cache table.

void init (TXmlElement $config)

- TXmlElement $config: configuration for this module, can be null

Redefinition of:

TCache::init()
  Initializes the cache module.

setAutoCreateCacheTable (line 311)

- access: public
- see: TDbCache::setCacheTableName()

void setAutoCreateCacheTable (boolean $value)

- boolean $value: whether the cache DB table should be automatically created if not exists.

setCacheTableName (line 293)

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: (itemkey CHAR(128) PRIMARY KEY, value BLOB, expire INT) 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.)

- access: public
- see: TDbCache::setAutoCreateCacheTable()

void setCacheTableName (string $value)

- string $value: the name of the DB table to store cache content

setConnectionID (line 219)

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.

- access: public
- since: 3.1.1

void setConnectionID (string $value)

- string $value: ID of the TDataSourceConfig module

setConnectionString (line 236)

- access: public
- see: http://www.php.net/manual/en/function.pdo-construct.php

void setConnectionString (string $value)

- string $value: The Data Source Name, or DSN, contains the information required to connect to the database.

setPassword (line 268)

- access: public

void setPassword (string $value)

- string $value: the password for establishing DB connection

setUsername (line 252)

- access: public

void setUsername (string $value)

- string $value: the username for establishing DB connection

setValue (line 337)

Stores a value identified by a key in cache.

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

- return: true if the value is successfully stored into cache, false otherwise
- access: protected

boolean setValue (string $key, string $value, integer $expire)

- string $key: the key identifying the value to be cached
- string $value: the value to be cached
- integer $expire: the number of seconds in which the cached value will expire. 0 means never expire.

Redefinition of:

TCache::setValue()
  Stores a value identified by a key in cache.

#### Inherited Methods

Inherited From TCache

> TCache::add()
> TCache::addValue()
> TCache::delete()
> TCache::deleteValue()
> TCache::flush()
> TCache::generateUniqueKey()
> TCache::get()
> TCache::getKeyPrefix()
> TCache::getPrimaryCache()
> TCache::getValue()
> TCache::init()
> TCache::offsetExists()
> TCache::offsetGet()
> TCache::offsetSet()
> TCache::offsetUnset()
> TCache::set()
> TCache::setKeyPrefix()
> TCache::setPrimaryCache()
> TCache::setValue()

Inherited From TModule

> TModule::getID()
> TModule::init()
> TModule::setID()

Inherited From TApplicationComponent

> TApplicationComponent::getApplication()
> TApplicationComponent::getRequest()
> TApplicationComponent::getResponse()
> TApplicationComponent::getService()
> TApplicationComponent::getSession()
> TApplicationComponent::getUser()
> TApplicationComponent::publishAsset()
> TApplicationComponent::publishFilePath()

Inherited From TComponent

> TComponent::addParsedObject()
> TComponent::attachEventHandler()
> TComponent::canGetProperty()
> TComponent::canSetProperty()
> TComponent::createdOnTemplate()
> TComponent::detachEventHandler()
> TComponent::evaluateExpression()
> TComponent::evaluateStatements()
> TComponent::getEventHandlers()
> TComponent::getSubProperty()
> TComponent::hasEvent()
> TComponent::hasEventHandler()
> TComponent::hasProperty()
> TComponent::raiseEvent()
> TComponent::setSubProperty()
> TComponent::__get()
> TComponent::__set()

Documentation generated on Sun, 11 Jan 2009 20:22:16 -0500 by phpDocumentor 1.3.0RC4