Optimizing plugin performance by storing external data using transients

Some WordPress functions, such as the fetch_feed function that we saw in the Displaying RSS items from an external feed recipe, offer a built-in caching mechanism. This is not the case when building custom code to retrieve information from other online data sources. The following recipe takes a look at using the public API of a transportation agency, Bay Area Rapid Transit, in the San Francisco area. It shows how to retrieve and cache remote XML data in our local site database using transients to speed up site performance while also alleviating the load on the remote data source.

Getting ready

You should have access to a WordPress development environment.

How to do it...

Follow these steps to query, cache, and display transit data from an external source:

1. Navigate to the WordPress plugins directory of your development installation.
2. Create a new directory called ch11-transit-feed.
3. Navigate...