Background Caching with Transients Example

example.php

<?php
/*
 * Background Caching with Transients
 * Using BBC News API as an example
 */

function pb_get_news() {

    /*
     * Get transient and if expired refresh data immediately
     */
    if ( false === ( $news = get_transient( 'pb_bbc_news' ) ) ) {

        // Uses BBC News API to fetch new data
        $news = pb_refresh_news();
        
    }

    /*
     * Check if News has soft expired, if so run refresh after page load.
     */
    elseif ( $news->expiry < time() ) {

        // Add 60 seconds to soft expire, to stop other threads trying to update it at the same time.
        $news->expiry = ( time() + 60 );

        /*
         * Update soft expire time.
         */
        set_transient( 'pb_bbc_news', $news, 24 * HOUR_IN_SECONDS );

        // Set the refresh function to run just before PHP shutsdown.
        add_action( 'shutdown', 'pb_refresh_news' );
        
    }
    
    return $news;
    
}

/*
 * Refreshes the Transient data.
 */
function pb_refresh_news() {

    // Make HTTP request to BBC News API.
    $response = wp_remote_request( 'http://api.bbcnews.appengine.co.uk/stories/headlines' );

    // Response is in JSON format, so decode it.
    $news = json_decode( $response['body'] );

    // Add custom expiry time
    // MINUTE_IN_SECONDS and the other similar constants are all included in WordPress.
    $news->expiry = time() + ( 5 * MINUTE_IN_SECONDS );

    // Set transient with latest News data
    set_transient( 'pb_bbc_news', $news, 24 * HOUR_IN_SECONDS );
    
    return $news;
    
}

/*
 * Display BBC News Headlines
 */
function pb_display_news() {

    // Get the News data
    $headlines = pb_get_news();
    ?>
    
    <ul class="news-container">

    <?php foreach ( $headlines->stories as $headline ) { ?>
        
        <li>
            <h3>
                <a href="<?php echo $headline->link; ?>" title="<?php echo $headline->title; ?>">
                    <?php echo $headline->title; ?>
                </a>
            </h3>
            <p>
                <img src="<?php echo $headline->thumbnail; ?>" alt="<?php echo $headline->title; ?>" />
                <?php echo $headline->description; ?>
            </p>
        </li>
        
    <?php } ?>

    </ul>

<?php
    
}