自定义缓存实现 {/programmers/caching/caching-custom/}
作为使用默认的基于文件的缓存机制的替代方案，你可以指定一个自定义的缓存实现，用于读取、写入和清除缓存文件。
注意
在 Smarty2 中，这个功能由一个名为
$cache_handler_func的回调函数实现。Smarty3 用Smarty_CacheResource模块替换了这个回调。
使用自定义缓存实现，你可能试图实现以下至少一项目标：用更快的存储引擎替换慢的文件系统，使缓存可被多个服务器访问。
Smarty 允许 CacheResource 实现使用Smarty_CacheResource_Custom或Smarty_CacheResource_KeyValueStore其中一个 API。Smarty_CacheResource_Custom是一个简单的 API，将所有的读、写、清除调用都指向你的实现。这个 API 允许你以你认为合适的方式存储在任何地方。Smarty_CacheResource_KeyValueStoreAPI 允许你将任何"简单"的键值存储（如 APC，Memcache，...）转变为一个功能全面的 CacheResource 实现。也就是说，你可以处理像"a|b|c"这样的深层缓存组，以一种可以清除缓存组"a"和所有嵌套组的方式处理它 - 尽管键值存储本质上不允许这种类型的层次结构。
自定义 CacheResources 可以放在你的$plugins_dir中的一个文件cacheresource.foobarxyz.php中，或者在运行时使用registerCacheResource()注册。在任何情况下，你都需要设置$caching_type来调用你的自定义 CacheResource 实现。
以下是一个使用 MySQL 作为 Smarty 的输出缓存存储资源的例子：
<?php
require_once 'libs/Smarty.class.php';
$smarty = new Smarty();
$smarty->caching_type = 'mysql';
/**
* MySQL CacheResource
*
* CacheResource Implementation based on the Custom API to use
* MySQL as the storage resource for Smarty's output caching.
*
* Table definition:
* <pre>CREATE TABLE IF NOT EXISTS `output_cache` (
* `id` CHAR(40) NOT NULL COMMENT 'sha1 hash',
* `name` VARCHAR(250) NOT NULL,
* `cache_id` VARCHAR(250) NULL DEFAULT NULL,
* `compile_id` VARCHAR(250) NULL DEFAULT NULL,
* `modified` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
* `content` LONGTEXT NOT NULL,
* PRIMARY KEY (`id`),
* INDEX(`name`),
* INDEX(`cache_id`),
* INDEX(`compile_id`),
* INDEX(`modified`)
* ) ENGINE = InnoDB;</pre>
*
* @package CacheResource-examples
* @author Rodney Rehm
*/
class Smarty_CacheResource_Mysql extends Smarty_CacheResource_Custom {
// PDO instance
protected $db;
protected $fetch;
protected $fetchTimestamp;
protected $save;
public function __construct() {
try {
$this->db = new PDO("mysql:dbname=test;host=127.0.0.1", "smarty", "smarty");
} catch (PDOException $e) {
throw new SmartyException('Mysql Resource failed: ' . $e->getMessage());
}
$this->fetch = $this->db->prepare('SELECT modified, content FROM output_cache WHERE id = :id');
$this->fetchTimestamp = $this->db->prepare('SELECT modified FROM output_cache WHERE id = :id');
$this->save = $this->db->prepare('REPLACE INTO output_cache (id, name, cache_id, compile_id, content)
VALUES (:id, :name, :cache_id, :compile_id, :content)');
}
/**
* fetch cached content and its modification time from data source
*
* @param string $id unique cache content identifier
* @param string $name template name
* @param string $cache_id cache id
* @param string $compile_id compile id
* @param string $content cached content
* @param integer $mtime cache modification timestamp (epoch)
* @return void
*/
protected function fetch($id, $name, $cache_id, $compile_id, &$content, &$mtime)
{
$this->fetch->execute(array('id' => $id));
$row = $this->fetch->fetch();
$this->fetch->closeCursor();
if ($row) {
$content = $row['content'];
$mtime = strtotime($row['modified']);
} else {
$content = null;
$mtime = null;
}
}
/**
* Fetch cached content's modification timestamp from data source
*
* @note implementing this method is optional. Only implement it if modification times can be accessed faster than loading the complete cached content.
* @param string $id unique cache content identifier
* @param string $name template name
* @param string $cache_id cache id
* @param string $compile_id compile id
* @return integer|boolean timestamp (epoch) the template was modified, or false if not found
*/
protected function fetchTimestamp($id, $name, $cache_id, $compile_id)
{
$this->fetchTimestamp->execute(array('id' => $id));
$mtime = strtotime($this->fetchTimestamp->fetchColumn());
$this->fetchTimestamp->closeCursor();
return $mtime;
}
/**
* Save content to cache
*
* @param string $id unique cache content identifier
* @param string $name template name
* @param string $cache_id cache id
* @param string $compile_id compile id
* @param integer|null $exp_time seconds till expiration time in seconds or null
* @param string $content content to cache
* @return boolean success
*/
protected function save($id, $name, $cache_id, $compile_id, $exp_time, $content)
{
$this->save->execute(array(
'id' => $id,
'name' => $name,
'cache_id' => $cache_id,
'compile_id' => $compile_id,
'content' => $content,
));
return !!$this->save->rowCount();
}
/**
* Delete content from cache
*
* @param string $name template name
* @param string $cache_id cache id
* @param string $compile_id compile id
* @param integer|null $exp_time seconds till expiration or null
* @return integer number of deleted caches
*/
protected function delete($name, $cache_id, $compile_id, $exp_time)
{
// delete the whole cache
if ($name === null && $cache_id === null && $compile_id === null && $exp_time === null) {
// returning the number of deleted caches would require a second query to count them
$query = $this->db->query('TRUNCATE TABLE output_cache');
return -1;
}
// build the filter
$where = array();
// equal test name
if ($name !== null) {
$where[] = 'name = ' . $this->db->quote($name);
}
// equal test compile_id
if ($compile_id !== null) {
$where[] = 'compile_id = ' . $this->db->quote($compile_id);
}
// range test expiration time
if ($exp_time !== null) {
$where[] = 'modified < DATE_SUB(NOW(), INTERVAL ' . intval($exp_time) . ' SECOND)';
}
// equal test cache_id and match sub-groups
if ($cache_id !== null) {
$where[] = '(cache_id = '. $this->db->quote($cache_id)
. ' OR cache_id LIKE '. $this->db->quote($cache_id .'|%') .')';
}
// run delete query
$query = $this->db->query('DELETE FROM output_cache WHERE ' . join(' AND ', $where));
return $query->rowCount();
}
}
以下是一个使用 memcache 作为 Smarty 的输出缓存存储资源的例子：
<?php
require_once 'libs/Smarty.class.php';
$smarty = new Smarty();
$smarty->caching_type = 'memcache';
/**
* Memcache CacheResource
*
* CacheResource Implementation based on the KeyValueStore API to use
* memcache as the storage resource for Smarty's output caching.
*
* Note that memcache has a limitation of 256 characters per cache-key.
* To avoid complications all cache-keys are translated to a sha1 hash.
*
* @package CacheResource-examples
* @author Rodney Rehm
*/
class Smarty_CacheResource_Memcache extends Smarty_CacheResource_KeyValueStore {
/**
* memcache instance
* @var Memcache
*/
protected $memcache = null;
public function __construct()
{
$this->memcache = new Memcache();
$this->memcache->addServer( '127.0.0.1', 11211 );
}
/**
* Read values for a set of keys from cache
*
* @param array $keys list of keys to fetch
* @return array list of values with the given keys used as indexes
* @return boolean true on success, false on failure
*/
protected function read(array $keys)
{
$_keys = $lookup = array();
foreach ($keys as $k) {
$_k = sha1($k);
$_keys[] = $_k;
$lookup[$_k] = $k;
}
$_res = array();
$res = $this->memcache->get($_keys);
foreach ($res as $k => $v) {
$_res[$lookup[$k]] = $v;
}
return $_res;
}
/**
* Save values for a set of keys to cache
*
* @param array $keys list of values to save
* @param int $expire expiration time
* @return boolean true on success, false on failure
*/
protected function write(array $keys, $expire=null)
{
foreach ($keys as $k => $v) {
$k = sha1($k);
$this->memcache->set($k, $v, 0, $expire);
}
return true;
}
/**
* Remove values from cache
*
* @param array $keys list of keys to delete
* @return boolean true on success, false on failure
*/
protected function delete(array $keys)
{
foreach ($keys as $k) {
$k = sha1($k);
$this->memcache->delete($k);
}
return true;
}
/**
* Remove *all* values from cache
*
* @return boolean true on success, false on failure
*/
protected function purge()
{
return $this->memcache->flush();
}
}