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# Multiple Caches Per Page

You can have multiple cache files for a single call to display() or fetch(). Let's say that a call to display('index.tpl') may have several different output contents depending on some condition, and you want separate caches for each one. You can do this by passing a cache_id as the second parameter to the function call.

Example 13-6. passing a cache_id to display()
`<?php require('Smarty.class.php'); $smarty = new Smarty; $smarty->caching = true; $my_cache_id = $_GET['article_id']; $smarty->display('index.tpl',$my_cache_id); ?>`

Above, we are passing the variable $my_cache_id to display() as the cache_id. For each unique value of $my_cache_id, a separate cache will be generated for index.tpl. In this example, "article_id" was passed in the URL and is used as the cache_id.

> Technical Note: Be very cautious when passing values from a client (web browser) into Smarty (or any PHP application.) Although the above example of using the article_id from the URL looks handy, it could have bad consequences. The cache_id is used to create a directory on the file system, so if the user decided to pass an extremely large value for article_id, or write a script that sends random article_ids at a rapid pace, this could possibly cause problems at the server level. Be sure to sanitize any data passed in before using it. In this instance, maybe you know the article_id has a length of 10 characters and is made up of alpha-numerics only, and must be a valid article_id in the database. Check for this!

Be sure to pass the same cache_id as the second parameter to is_cached() and clear_cache().

Example 13-7. passing a cache_id to is_cached()
`<?php require('Smarty.class.php'); $smarty = new Smarty; $smarty->caching = true; $my_cache_id = $_GET['article_id']; if(!$smarty->is_cached('index.tpl',$my_cache_id)) { // No cache available, do variable assignments here. $contents = get_database_contents(); $smarty->assign($contents); } $smarty->display('index.tpl',$my_cache_id); ?>`

You can clear all caches for a particular cache_id by passing null as the first parameter to clear_cache().

Example 13-8. clearing all caches for a particular cache_id
`<?php require('Smarty.class.php'); $smarty = new Smarty; $smarty->caching = true; // clear all caches with "sports" as the cache_id $smarty->clear_cache(null,"sports"); $smarty->display('index.tpl',"sports"); ?>`

In this manner, you can "group" your caches together by giving them the same cache_id.

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