How to Show Recent Posts Using Shortcode with Transient Caching in WordPress

<?php
/**
 * Recent Posts with 24-Hour Caching
 * Add this code to your theme's functions.php file
 */

// Register the shortcode
add_shortcode('recent_posts_cached', 'display_cached_recent_posts');

function display_cached_recent_posts($atts) {
    
    // Shortcode attributes with defaults
    $atts = shortcode_atts(array(
        'posts_per_page' => 5,
        'show_excerpt' => 'yes',
        'show_image' => 'yes',
        'cache_hours' => 24
    ), $atts);
    
    // Create unique cache key
    $cache_key = 'recent_posts_' . md5(serialize($atts));
    
    // Convert hours to seconds
    $cache_time = intval($atts['cache_hours']) * 3600;
    
    // Try to get cached data
    $cached_posts = get_transient($cache_key);
    
    if ($cached_posts === false) {
        // NO CACHE FOUND - Let's create it!
        
        // Query the database
        $recent_posts = new WP_Query(array(
            'post_type' => 'post',
            'post_status' => 'publish',
            'posts_per_page' => $atts['posts_per_page'],
            'orderby' => 'date',
            'order' => 'DESC'
        ));
        
        // Store posts in cache
        set_transient($cache_key, $recent_posts, $cache_time);
        
        // Add HTML comment for debugging
        $output = "<!-- Cache MISS - Generated fresh at " . date('Y-m-d H:i:s') . " -->";
    } else {
        // CACHE FOUND! Using cached version
        $recent_posts = $cached_posts;
        
        // Add HTML comment for debugging
        $output = "<!-- Cache HIT - Using cached data from " . date('Y-m-d H:i:s') . " -->";
    }
    
    // Start building the HTML output
    $output .= '<div class="cached-recent-posts">';
    $output .= '<div class="posts-grid">';
    
    if ($recent_posts->have_posts()) {
        while ($recent_posts->have_posts()) {
            $recent_posts->the_post();
            
            $output .= '<article class="post-item">';
            
            // Show featured image if enabled
            if ($atts['show_image'] === 'yes' && has_post_thumbnail()) {
                $output .= '<div class="post-thumbnail">';
                $output .= '<a href="' . get_permalink() . '">';
                $output .= get_the_post_thumbnail(get_the_ID(), 'medium');
                $output .= '</a>';
                $output .= '</div>';
            }
            
            // Post title
            $output .= '<h3 class="post-title">';
            $output .= '<a href="' . get_permalink() . '">' . get_the_title() . '</a>';
            $output .= '</h3>';
            
            // Post date
            $output .= '<div class="post-meta">';
            $output .= '<span class="post-date">📅 ' . get_the_date() . '</span>';
            $output .= '</div>';
            
            // Post excerpt if enabled
            if ($atts['show_excerpt'] === 'yes') {
                $output .= '<div class="post-excerpt">';
                $output .= wp_trim_words(get_the_excerpt(), 20, '...');
                $output .= '</div>';
            }
            
            // Read more link
            $output .= '<a href="' . get_permalink() . '" class="read-more">Read More →</a>';
            
            $output .= '</article>';
        }
        wp_reset_postdata();
    } else {
        $output .= '<p>No posts found.</p>';
    }
    
    $output .= '</div>';
    $output .= '</div>';
    
    return $output;
}

/**
 * Clear cache when new post is published
 * This ensures fresh content appears immediately
 */
function clear_recent_posts_cache_on_update($post_id) {
    // Don't clear for autosaves
    if (wp_is_post_autosave($post_id)) {
        return;
    }
    
    // Don't clear for revisions
    if (wp_is_post_revision($post_id)) {
        return;
    }
    
    // Clear ALL recent posts caches
    global $wpdb;
    $wpdb->query("DELETE FROM {$wpdb->options} WHERE option_name LIKE '_transient_recent_posts_%'");
    $wpdb->query("DELETE FROM {$wpdb->options} WHERE option_name LIKE '_transient_timeout_recent_posts_%'");
}

// Hook into post save actions
add_action('save_post', 'clear_recent_posts_cache_on_update');
add_action('publish_post', 'clear_recent_posts_cache_on_update');
add_action('delete_post', 'clear_recent_posts_cache_on_update');

/* Recent Posts with Caching Styles */
.cached-recent-posts {
    margin: 30px 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
}

.posts-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 30px;
}

.post-item {
    background: #ffffff;
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.post-item:hover {
    transform: translateY(-5px);
    box-shadow: 0 5px 20px rgba(0,0,0,0.15);
}

.post-thumbnail img {
    width: 100%;
    height: 200px;
    object-fit: cover;
}

.post-title {
    margin: 15px 20px 10px;
    font-size: 1.25rem;
}

.post-title a {
    color: #2c3e50;
    text-decoration: none;
}

.post-title a:hover {
    color: #3498db;
}

.post-meta {
    margin: 0 20px 10px;
    color: #7f8c8d;
    font-size: 0.85rem;
}

.post-excerpt {
    margin: 0 20px 15px;
    color: #555;
    line-height: 1.6;
    font-size: 0.9rem;
}

.read-more {
    display: inline-block;
    margin: 0 20px 20px;
    color: #3498db;
    text-decoration: none;
    font-weight: 600;
}

.read-more:hover {
    color: #2980b9;
}

@media (max-width: 768px) {
    .posts-grid {
        grid-template-columns: 1fr;
        gap: 20px;
    }
}

// Add admin bar button to clear cache
add_action('admin_bar_menu', 'add_clear_cache_button', 100);
function add_clear_cache_button($wp_admin_bar) {
    if (!current_user_can('manage_options')) {
        return;
    }
    
    $wp_admin_bar->add_node(array(
        'id' => 'clear-posts-cache',
        'title' => '🗑️ Clear Posts Cache',
        'href' => wp_nonce_url(admin_url('admin-post.php?action=clear_posts_cache'), 'clear_cache_action')
    ));
}

// Handle cache clearing
add_action('admin_post_clear_posts_cache', 'handle_clear_cache');
function handle_clear_cache() {
    if (!wp_verify_nonce($_GET['_wpnonce'], 'clear_cache_action')) {
        wp_die('Security check failed');
    }
    
    global $wpdb;
    $wpdb->query("DELETE FROM {$wpdb->options} WHERE option_name LIKE '_transient_recent_posts_%'");
    
    wp_redirect($_SERVER['HTTP_REFERER']);
    exit;
}