Lifetimes

A lifetime is how long a cached value stays valid. Once it expires, get() returns null and the caller has to calculate the value again.

Create a Snippet¶

Create a Snippet named testCache with this code:

<?php
$cacheManager = $modx->getCacheManager();

$lifetime = 10; // in seconds

if (!$payload = $cacheManager->get('my_cache_key')) {
    $payload = date('H:i:s');
    $cacheManager->set('my_cache_key',$payload, $lifetime);
}

return $payload;

The value is written on the first request and read on every request after that, until the lifetime runs out and get() returns null again.

Reference the Snippet¶

A Snippet that manages its own caching must be called uncached. The uncached call bypasses the standard Resource caching, so your code stays in control of the value.

[[!testCache]]

Observations¶

Open the Resource that calls testCache and refresh it repeatedly. The timestamp changes only once every 10 seconds.

This Snippet writes to the default partition, so clearing the site cache clears it too. That is why the original 10-second lifetime is hard to observe: you get a fresh 10 seconds each time you clear the cache. Raise $lifetime to 60 seconds to watch it expire without clearing.

Data in a partition of your own survives clearing the site cache: refresh() clears the fixed list of core partitions, and a partition that is not on that list is never touched. Pass the partition in $options — see Programmatic (Custom) Caching.

Summary¶

A lifetime is worth setting when the value is expensive to calculate and stays correct for a while — an intensive database query, a slow API call. Caching it for a few seconds keeps that work off every request.