1. Introduction to the
WordPress Transients API
Subtitle goes here if needed
Presenter
Topher DeRosia
@topher1kenobe
Date
20 July, 2019

2. What is a Transient, and where would I use it?
Time consuming queries
Meta queries are slow. Meta queries comparing against multiple fields
are even slower. We can cache the results in a transient.
Remote data fetched via the HTTP API
Using the HTTP API you can fetch data from a remote server. But
what if that server goes down? What about latency? We can cache
the results in a transient.
tran·sient /ˈtranSHənt,ˈtranzēənt/
adjective: transient
1. lasting only for a short time; impermanent. "a transient cold spell"
2. In WordPress, a bit of data cached for an indeterminate amount of time

3. How do transients work?
• Each transient has a name
• When you need the data, check to see if it exists
• If it does, use it.
• If it doesn’t, generate the data and set it for next time

4. Where are transients stored?
• I don’t care
• It doesn’t matter
• WordPress takes care of it for you

5. No, really, where are transients stored?
• First WordPress looks for a real, system level, caching module like
memcached, Redis, APC, Varnish, etc. These are very very fast, and
much prefered.
• Failing that, transients are store in the WordPress options table. Yes, this
is still a database call, but a simple, speedy one.
• You don’t have to do anything to set this up, WordPress magically handles
it.

6. How is this magic accomplished?
• WordPress provides functions to set, get, and delete transients. Setting
one that already exists updates it.
• Using these function you simply ask for the data you want. If it’s not there
you build it and store it for next time.

8. Behold the horrible query.
$args = [
'post_status'=> 'publish',
'post_type' => 'coaches',
'orderby' => 'date',
'no_found_rows' => true,
'meta_query' => [
[
['key'] = 'ecpt_sold';
['value'] = 'on';
['compare'] = 'NOT EXISTS';
],
],
'meta_query' => [
[
['key'] = 'ecpt_featured';
['value'] = 'on';
['compare'] = 'EXISTS';
],
],
];
$coaches_query = new WP_Query( $args );

9. Behold the transient code.
// create the transient name
$transient_name = 'coaches';
// try getting the transient.
$coaches = get_transient( $transient_name );
// if the get works properly, I should have an object in $coaches.
// If not, run the query.
if( ! is_object( $coaches ) ) {
// run horrible query here
$coaches_query = new WP_Query( $args );
// save the results of the query with a 12 hour timeout
$save_query = set_transient( $transient_name, $coaches_query, HOUR_IN_SECONDS * 12 );
$coaches = $coaches_query;
}
// now $coaches will always hold an object full of Coach

10. But wait! What about changes?
// delete featured coaches transient on coach save
function delete_coach_transient( $post_id ) {
// First we want to make sure that this is a real save, not simply an auto save
if ( ! wp_is_post_revision( $post_id ) ) {
// now we declare our custom content type, because we only want to run this on the save of this type
$slug = 'coaches';
// this is where we actually make sure we're on the right type.
$_POST += array( "{$slug}_edit_nonce" => '' );
if ( $slug != $_POST['post_type'] ) {
return;
}
// assuming we're on the proper type, set the transient name
$transient_name = 'coaches';
// now delete the actual transient
delete_transient($transient_name);
}
// end delete_featured_transient
}
// now we hook that function into save_post and it's all set
add_action('save_post','delete_coach_transient');

11. Important things to remember
• You can store just about anything in a transient
• Transients are ethereal. Lots of things can delete them, never assume
they’re there just because you set them. ALWAYS TEST
• Think about when and how to invalidate them. Otherwise you’re stuck with
cached content

12. Resources
• Pippin’s Transients Manager
https://wordpress.org/plugins/transients-manager/
• Delete Expired Transients
https://wordpress.org/plugins/delete-expired-transients/
• Query Monitor
https://wordpress.org/plugins/query-monitor/

13. Thank You
Twitter: @topher1kenobe
Make WordPress Slack: topher1kenobe
Email: topher@bigcommerce.com