The Transients API is 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 temporarily store cached information. WordPress Transients API, which offers a simple and standardized way of storing cached data in the database temporarily by giving it a custom name and a timeframe after which it will expire and be deleted.

Saving Transients

To save a transient you use set_transient() :

$transient

(string) Transient name. Expected to not be SQL-escaped. Must be 172 characters or fewer in length.

$value

(array|object) Data to save, either a regular variable or an array/object. The API will handle serialization of complex data for you.

$expiration

(integer) The maximum of seconds to keep the data before refreshing. Transients may expire before the $expiration (Due to External Object Caches, or database upgrades) but will never return their value past $expiration.

So for example to save the $special_query_results object for 12 hours you would do:

Using Time Constants

So for example, the code sample from above can be simplified to:

Fetching Transients

To get a saved transient you use get_transient() :

• $transient the unique slug used while saving the transient with set_transient().

In our case we could fetch our special query results with:

If the transient does not exist, or has expired, then get_transient() will return false. This should be checked using the identity operator (===) instead of the normal equality operator (==), because an integer value of zero (or other “empty”/”falsey” data) could be the data you’re wanting to store. Because of this “false” value, transients should not be used to hold plain boolean values (true/false). Put them into an array or convert them to integers instead.

Example usage:

The above code will get the transient and put it into $value. The code inside the if block only runs when there’s not a valid transient for it to get. This is typically a method to re-generate the transient value through other means. Keep in mind that it’s possible for a transient to not be available before it’s normal expiration time.

Removing Saved Transients

Our transient will die naturally of old age once $expiration seconds have passed since we last ran set_transient(), but we can force the transient to die early by manually deleting it. This is useful for times when a given activity (saving a post, adding a category etc.) will make the cached data inherently stale and in need of updating.

• $transient the unique name used when saving with set_transient().

In our case, obviously, this would be:

WordPress infrequently cleans out expired transients. To prevent expired transients from building up in the database, it’s a good practice to always remove your transient once you are done with it and no longer need it.