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# Cache Handler Function

As an alternative to using the default file-based caching mechanism, you can specify a custom cache handling function that will be used to read, write and clear cached files.

Create a function in your application that Smarty will use as a cache handler. Set the name of it in the $cache_handler_func class variable. Smarty will now use this to handle cached data. The first argument is the action, which will be one of 'read', 'write' and 'clear'. The second parameter is the Smarty object. The third parameter is the cached content. Upon a write, Smarty passes the cached content in these parameters. Upon a 'read', Smarty expects your function to accept this parameter by reference and populate it with the cached data. Upon a 'clear', pass a dummy variable here since it is not used. The fourth parameter is the name of the template file (needed for read/write), the fifth parameter is the cache_id (optional), and the sixth is the compile_id (optional).

Note: The last parameter ($exp_time) was added in Smarty-2.6.0.

Example 14-5. example using MySQL as a cache source
`<?php /* example usage: include('Smarty.class.php'); include('mysql_cache_handler.php'); $smarty = new Smarty; $smarty->cache_handler_func = 'mysql_cache_handler'; $smarty->display('index.tpl'); mysql database is expected in this format: create database SMARTY_CACHE; create table CACHE_PAGES( CacheID char(32) PRIMARY KEY, CacheContents MEDIUMTEXT NOT NULL ); */ function mysql_cache_handler($action, &$smarty_obj, &$cache_content, $tpl_file=null, $cache_id=null, $compile_id=null, $exp_time=null) { // set db host, user and pass here $db_host = 'localhost'; $db_user = 'myuser'; $db_pass = 'mypass'; $db_name = 'SMARTY_CACHE'; $use_gzip = false; // create unique cache id $CacheID = md5($tpl_file.$cache_id.$compile_id); if(! $link = mysql_pconnect($db_host, $db_user, $db_pass)) { $smarty_obj->_trigger_error_msg("cache_handler: could not connect to database"); return false; } mysql_select_db($db_name); switch ($action) { case 'read': // read cache from database $results = mysql_query("select CacheContents from CACHE_PAGES where CacheID='$CacheID'"); if(!$results) { $smarty_obj->_trigger_error_msg("cache_handler: query failed."); } $row = mysql_fetch_array($results,MYSQL_ASSOC); if($use_gzip && function_exists("gzuncompress")) { $cache_contents = gzuncompress($row["CacheContents"]); } else { $cache_contents = $row["CacheContents"]; } $return = $results; break; case 'write': // save cache to database if($use_gzip && function_exists("gzcompress")) { // compress the contents for storage efficiency $contents = gzcompress($cache_content); } else { $contents = $cache_content; } $results = mysql_query("replace into CACHE_PAGES values( '$CacheID', '".addslashes($contents)."') "); if(!$results) { $smarty_obj->_trigger_error_msg("cache_handler: query failed."); } $return = $results; break; case 'clear': // clear cache info if(empty($cache_id) && empty($compile_id) && empty($tpl_file)) { // clear them all $results = mysql_query("delete from CACHE_PAGES"); } else { $results = mysql_query("delete from CACHE_PAGES where CacheID='$CacheID'"); } if(!$results) { $smarty_obj->_trigger_error_msg("cache_handler: query failed."); } $return = $results; break; default: // error, unknown action $smarty_obj->_trigger_error_msg("cache_handler: unknown action \"$action\""); $return = false; break; } mysql_close($link); return $return; } ?>`

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