smarty/docs/en/programmers/caching/caching-multiple-caches.xml

<?xml version="1.0" encoding="iso-8859-1"?>
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   <sect1 id="caching.multiple.caches">
    <title>Multiple Caches Per Page</title>
    <para>
     You can have multiple cache files for a single call to
     <link linkend="api.display">display()</link>
     or <link linkend="api.fetch">fetch()</link>.
     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.
    </para>
    <example>
     <title>passing a cache_id to display()</title>
     <programlisting role="php">
<![CDATA[
<?php
require('Smarty.class.php');
$smarty = new Smarty;

$smarty->caching = true;

$my_cache_id = $_GET['article_id'];

$smarty->display('index.tpl',$my_cache_id);
?>
]]>
     </programlisting>
    </example>
    <para>
     Above, we are passing the variable $my_cache_id to
     <link linkend="api.display">display()</link>
     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.
    </para>
    <note>
     <title>Technical Note</title>
     <para>
      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!
     </para>
    </note>
    <para>
     Be sure to pass the same cache_id as the
     second parameter to <link linkend="api.is.cached">is_cached()</link> and
     <link linkend="api.clear.cache">clear_cache()</link>.
    </para>
    <example>
     <title>passing a cache_id to is_cached()</title>
     <programlisting role="php">
<![CDATA[
<?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);
?>
]]>
     </programlisting>
    </example>
    <para>
     You can clear all caches for a particular cache_id by passing null as the
     first parameter to
     <link linkend="api.clear.cache">clear_cache()</link>.
    </para>
    <example>
     <title>clearing all caches for a particular cache_id</title>
     <programlisting role="php">
<![CDATA[
<?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");
?>
]]>
     </programlisting>
    </example>
    <para>
     In this manner, you can "group" your caches together by giving them the
     same cache_id.
    </para>
    
   </sect1>
   
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