The Transient API in WordPress is one of the many APIs available in the WordPress core that, once used, become invaluable and used on a daily basis. This is a quick guide to getting started with the transients API, when to use it and why.

The Transients API, while similar to the WordPress options API, has the addition of an expiry time. The API is used to store data in the database for a fix amount of time, at which point it is deleted and would need to be re-added, if one requires the data again. The WordPress Codex explains the Transients API as:

…very similar to the Options API but with the added feature of an expiration time, which simplifies the process of using the wp_options database table to store cached information.

From a technical standpoint, transients are also sped up by caching plugins, which store the data in memory, rather than in the database, making for a faster lookup.

Getting started

Using transients is easier than you might think. The first thing to note is that there are two types of transients; conventional (only on the specified site within a WordPress multisite installation) and “site” (across the entire WordPress multisite installation). They interact in the same way though.

The Transients API has 3 core functions; set_transient(), get_transient() and delete_transient(). They function in the same way as add_option(), get_option() and delete_option() do, so they should be familiar.

Brief function analysis

set_transient()

Stores data in a transient.

The parameters are:

1. The transient key (the name of the transient to store the data in)
2. The value (the data to store)
3. The expiration (the time expiration, in seconds, from the time of storage – one day would be 60 * 60 * 24)

get_transient()

Retrieve the transient data, if it’s available.

The parameters are:

1. The transient key (the name of the transient the data is stored in)

delete_transient()

Force the expiry/removal of a specified transient.

The parameters are:

1. The transient key (the name of the transient the data is stored in)

The Transients API in use

To use the Transients API, the process is straight forward. Check if the transient is available. If it isn’t, get the data (this could be anything from a simple line of text -which may not be too practical- to an advanced and resource-intensive database query, which you may not want to run every time your website is loaded) and assign it to the transient. Assign the data to a variable and return it for use in your code.

In code, this may look like the following:

<?php
	$transient_key = 'my-transient-key';
	$data = get_transient( $transient_key );
	if ( $data == '' ) {
		$data = get_posts( array( 'posts_per_page' => -1 ) );
		set_transient( $transient_key, $data, 60 * 60 * 24 );
	}
	
	// You would then carry on using $data in your code.
?>

An example of when WordPress itself uses the Transients API is during checks for updates of themes, plugins and WordPress itself. These checks don’t in fact happen each time you visit the “Updates” dashboard screen, but periodically based on a transient of stored information about the themes and plugins you have in your installation.

Where and when to use the Transients API

Usage of this API is vast and varied. Essentially, the Transients API can be seen as a form of caching system with an expiry time. Therefore, you may want to cache data (for example, from an RSS feed or API request) for a few hours or days, or you could cache something for a few seconds while a user is busy on your website (to make their experience that little bit faster). With such simple implementation, the usage possibilities are limited only by one’s imagination and a coding project’s requirements.

Now that you know about the Transients API, I’m certain you’ll start using it more often to speed up your projects. This API, while seemingly so small and simple, is incredibly powerful and can transform bloated code into streamlined genius.