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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 optional `$cache_id`.

- The sixth is the optional `$compile_id`.

- The seventh and last parameter `$exp_time` was added in Smarty-2.6.0.

Example 15-5. 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')) { $cache_content = gzuncompress($row['CacheContents']); } else { $cache_content = $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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