WordPress Developer Reference & Cheatsheet

<?php
// Query products under $100 in the 'featured' category
$query = new WP_Query([
    'post_type'      => 'product',
    'posts_per_page' => 10,
    'meta_query'     => [
        ['key' => 'price', 'value' => 100, 'compare' => '<'],
    ],
    'tax_query' => [
        ['taxonomy' => 'category', 'field' => 'slug', 'terms' => 'featured'],
    ],
]);

if ($query->have_posts()) :
    while ($query->have_posts()) : $query->the_post(); ?>
        <h2><?php the_title(); ?></h2>
        <p>Price: <?php echo get_post_meta(get_the_ID(), 'price', true); ?></p>
    <?php endwhile;
    wp_reset_postdata();
endif;
?>

<?php
// Register a custom post type: Product
function register_product_post_type() {
    register_post_type('product', [
        'labels' => [
            'name'          => 'Products',
            'singular_name' => 'Product',
            'add_new_item'  => 'Add New Product',
        ],
        'public'       => true,
        'has_archive'  => true,
        'supports'     => ['title', 'editor', 'thumbnail', 'custom-fields', 'revisions'],
        'menu_icon'    => 'dashicons-cart',
        'rewrite'      => ['slug' => 'products'],
        'show_in_rest' => true,  // Enable Gutenberg and REST API
    ]);
}
add_action('init', 'register_product_post_type');

// Register a custom taxonomy: Brand
function register_brand_taxonomy() {
    register_taxonomy('brand', 'product', [
        'labels' => [
            'name'          => 'Brands',
            'singular_name' => 'Brand',
        ],
        'hierarchical' => true,  // Like categories (false = like tags)
        'rewrite'      => ['slug' => 'brand'],
        'show_in_rest' => true,
    ]);
}
add_action('init', 'register_brand_taxonomy');
?>

<?php
// === ACTIONS (do something) ===

// Enqueue scripts and styles
add_action('wp_enqueue_scripts', 'my_theme_assets');

// Run code when a post is published
add_action('publish_post', 'notify_on_publish', 10, 2);

// Add a custom dashboard widget
add_action('wp_dashboard_setup', 'add_custom_dashboard_widget');

// === FILTERS (modify something) ===

// Modify the post title
add_filter('the_title', function($title) {
    return '★ ' . $title;
});

// Change excerpt length
add_filter('excerpt_length', function() {
    return 30;
});

// Add custom classes to the body tag
add_filter('body_class', function($classes) {
    $classes[] = 'my-custom-class';
    return $classes;
});
?>

<?php
// Register custom REST endpoint: /myapp/v1/products/{id}
add_action('rest_api_init', function() {
    register_rest_route('myapp/v1', '/products/(?P<id>\d+)', [
        'methods'             => 'GET',
        'callback'            => function($data) {
            $post = get_post($data['id']);
            if (!$post || $post->post_type !== 'product') {
                return new WP_Error('not_found', 'Product not found', ['status' => 404]);
            }
            return [
                'id'          => $post->ID,
                'title'       => $post->post_title,
                'price'       => get_post_meta($post->ID, 'price', true),
                'brand'       => wp_get_post_terms($post->ID, 'brand', ['fields' => 'names']),
                'featured_image' => get_the_post_thumbnail_url($post->ID, 'full'),
            ];
        },
        'permission_callback' => '__return_true',
    ]);
});
?>

<?php
// functions.php — Standard theme setup
function my_theme_setup() {
    // Enable features
    add_theme_support('post-thumbnails');
    add_theme_support('custom-logo');
    add_theme_support('html5', ['search-form', 'comment-form', 'comment-list', 'gallery', 'caption']);
    add_theme_support('title-tag');

    // Register navigation menus
    register_nav_menus([
        'primary' => 'Primary Menu',
        'footer'  => 'Footer Menu',
    ]);
}
add_action('after_setup_theme', 'my_theme_setup');

// Load styles and scripts
function my_theme_assets() {
    wp_enqueue_style('main-style', get_stylesheet_uri(), [], wp_get_theme()->get('Version'));

    wp_enqueue_script(
        'main-js',
        get_template_directory_uri() . '/js/app.js',
        ['jquery'],
        wp_get_theme()->get('Version'),
        true  // Load in footer
    );

    // Pass data from PHP to JavaScript
    wp_localize_script('main-js', 'wpData', [
        'ajaxUrl'  => admin_url('admin-ajax.php'),
        'themeUrl' => get_template_directory_uri(),
    ]);
}
add_action('wp_enqueue_scripts', 'my_theme_assets');
?>

<?php
// wp-config.php additions (place before "That's all, stop editing!")

// Force admin over HTTPS
define('FORCE_SSL_ADMIN', true);

// Disable file editing from dashboard
define('DISALLOW_FILE_EDIT', true);

// Increase memory limit for complex operations
define('WP_MEMORY_LIMIT', '256M');
define('WP_MAX_MEMORY_LIMIT', '512M');

// Disable plugin/theme installation from dashboard (for locked-down sites)
define('DISALLOW_FILE_MODS', true);
?>