View source for Cache Basic API Guide

== Sample Module Code ==
=== Module Installation ===
Below is the code for a simple Joomla module that you can install and run to demonstrate the use of the Joomla cache functionality. If you are unsure about development and installing a Joomla module, following the tutorial at [[S:MyLanguage/J3.x:Creating a simple module/Introduction| Creating a simple module]] will help.

In a folder ''mod_demo_cache'' create these two files:

''mod_demo_cache.xml''
<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="utf-8"?>
<extension type="module" version="3.1" client="site" method="upgrade">
    <name>Cache demo</name>
    <version>1.0.1</version>
    <description>Code demonstrating use of Joomla Cache</description>
    <files>
        <filename module="mod_demo_cache">mod_demo_cache.php</filename>
    </files>
</extension>
</syntaxhighlight>

''mod_demo_cache.php''
<syntaxhighlight lang="php">
<?php
defined('_JEXEC') or die('Restricted Access');

use Joomla\CMS\Factory;

echo "<br>Current time is " . date("h:i:sa") . "<br>";

$cache = Factory::getCache('mod_demo_cache', 'callback');

$caching = $cache->getCaching();
if ($caching)
{
	echo "<br>Caching enabled<br>";
}
else
{
	echo "<br>Caching not enabled<br>";
}

$myquery = function ()
{	// This function calculates the biggest 3 tables from the selection below
	$tables = array("#__assets", "#__overrider", "#__content", "#__extensions", "#__menu", "#__updates", "#__ucm_history", "#__finder_terms_common");
	$db = Factory::getDbo();
	foreach ($tables as $name)
	{
		$query = $db->getQuery(true)
			->select('count(*)')
			->from($name);
		$db->setQuery($query);
		$totals["$name"] = $db->loadResult();
	}
	arsort($totals);
	return $totals;
};

$start = microtime(true);
try
{
	$results = $cache->get($myquery, array(), "top tables", false);
	$delay = microtime(true) - $start;
	echo "<br>$delay ms delay<br>";
}
catch (\JCacheException $cacheException)
{
	$results = $myquery();
	$delay = microtime(true) - $start;
	echo "<br>$delay ms delay (in cache exception)<br>";
}
echo "<h3>Top 3 tables</h3>";
$i = 0;
foreach ($results as $key => $value)
{
	echo "$key: $value<br>";
	$i++;
	if ($i == 3) break;
}
</syntaxhighlight>

Zip up the ''mod_demo_cache'' directory to create ''mod_demo_cache.zip''.

In your Joomla Administrator, go to Install Extensions and via the ''Upload Package File'' tab, select this zip file to install this sample cache module.

Make this module visible by editing it (click on it within the Modules page):
# making its status ''Published''
# selecting a position on the page for it to be shown
# on the menu assignment tab, specify the pages it should appear on

When you visit a site web page you should see the module in your selected position.

=== Module Explanation ===
The anonymous function assigned to ''$myquery'' performs ''SQL COUNT'' operations on a set of tables, and then reorders the resulting ''$totals'' array in size order, outputting the most populous three tables.

If caching is enabled, the results of running ''$myquery'' are stored in a cache file, and if you repeatedly reload the web page you will see the time difference in running the full query versus obtaining the results from cache.

The module also displays the current time. If when you reload the page the current time doesn't change, it means that the whole module output is being cached, and not being run on page reload. This will happen if:
* there is no user logged in, and
* either Progressive Cache is on or the System Page Cache plugin is enabled.
If Progressive Cache is on the output of all the modules are stored in cache (in the ''cache/com_modules'' directory), and upon page reload, the cache is used, rather than running the code of the individual modules.

If Page Cache is enabled, the whole web page is cached (in the ''cache/page'' directory).

It's instructive to experiment with the various cache settings, view the cache files in the file system and use the Administrator Clear Cache functionality to clear the cache for this specific module.