Week 23: WooCommerce Customization

1. The Data Model

WooCommerce doesn't reinvent WordPress's storage — it builds directly on top of the concepts from Weeks 17–21:

• Products — a product Custom Post Type (exactly Week 19's pattern), with price, SKU and stock stored as post meta, plus product_cat/product_tag custom taxonomies
• Orders — since WooCommerce 8+, stored in dedicated custom tables (wc_orders and related) rather than posts — WooCommerce's own version of Week 21's "when to use a custom table" decision, made at scale
• Customers — WordPress users (Week 13's wp_users), with WooCommerce-specific meta for billing/shipping addresses and order history

wp plugin install woocommerce --activate
wp plugin install storefront --activate # or any WooCommerce-compatible theme

<?php

$product = wc_get_product($productId); // never query product post meta directly -- use this

echo $product->get_name();
echo $product->get_price();
echo $product->is_in_stock() ? 'In stock' : 'Sold out';

wc_get_product() returns a proper WC_Product object with typed getter methods — the same discipline Week 17 recommended for wp_posts ("never query directly, use the API") applies just as strongly here, and matters even more given how much internal complexity WooCommerce's product data actually has (variations, stock management, tax classes).

2. Product Display Hooks

WooCommerce's product page is built from a dense sequence of actions — rather than overriding the whole template, you hook into (or remove) specific pieces:

<?php

function my_store_low_stock_badge() {
    global $product;

    if ($product->get_stock_quantity() <= 3 && $product->is_in_stock()) {
        echo '<p class="low-stock-badge">Only ' . $product->get_stock_quantity() . ' left!</p>';
    }
}
add_action('woocommerce_single_product_summary', 'my_store_low_stock_badge', 25);
// Priority 25 -- placed right after the price (priority 10) and before the add-to-cart form (30)

This is exactly Week 20's hook priority discussion, put to real use — WooCommerce documents the default priority of each piece of the product page precisely so extensions can insert new content at an exact position without touching core template files.

3. Cart & Checkout Hooks

Business logic around pricing and validation hooks into the cart and checkout lifecycle rather than the display layer:

<?php

function my_store_bulk_discount(\WC_Cart $cart) {
    foreach ($cart->get_cart() as $item) {
        if ($item['quantity'] >= 10) {
            $discounted = $item['data']->get_price() * 0.9; // 10% off, 10+ units
            $item['data']->set_price($discounted);
        }
    }
}
add_action('woocommerce_before_calculate_totals', 'my_store_bulk_discount');

function my_store_require_phone_at_checkout(array $fields): array {
    $fields['billing']['billing_phone']['required'] = true;
    return $fields; // a filter -- must return the (possibly modified) value
}
add_filter('woocommerce_checkout_fields', 'my_store_require_phone_at_checkout');

woocommerce_before_calculate_totals is an action (mutate the cart object, return nothing); woocommerce_checkout_fields is a filter (receive the fields array, return the modified version) — the exact action/filter distinction from Week 18, now applied to store-specific data.

4. The Order Lifecycle

An order moves through a defined sequence of statuses, and hooking status transitions is the standard way to trigger side effects — inventory updates, fulfillment emails, integrations with an external system:

pending → processing → completed
                    ↘ on-hold
                    ↘ cancelled / refunded / failed

<?php

function my_store_notify_fulfillment_on_processing(int $orderId) {
    $order = wc_get_order($orderId);

    wp_mail(
        'fulfillment@example.com',
        "New order #{$orderId} ready to fulfill",
        "Order total: " . $order->get_total()
    );
}
add_action('woocommerce_order_status_processing', 'my_store_notify_fulfillment_on_processing');

This is structurally identical to Week 16's Laravel TaskCompleted event pattern — a status transition is the "something happened" moment, and a hooked function is the "here's what should happen as a result," decoupled from wherever the status change originally occurred.

5. A Custom Extension

A "WooCommerce extension" is just Week 20's plugin pattern, targeting WooCommerce-specific hooks instead of core WordPress ones — nothing structurally new:

<?php
/**
 * Plugin Name: My Store Extras
 * Description: Bulk discounts and low-stock badges for the shop.
 * Version: 1.0.0
 */

if (!defined('ABSPATH')) exit;

// Good practice: confirm WooCommerce is actually active before hooking anything
add_action('plugins_loaded', function () {
    if (!class_exists('WooCommerce')) {
        return;
    }

    require_once __DIR__ . '/includes/product-display.php';
    require_once __DIR__ . '/includes/cart-rules.php';
});

Checking class_exists('WooCommerce') before hooking anything WooCommerce-specific matters: if a site administrator ever deactivates WooCommerce while this extension stays active, every hooked function referencing WC_Cart/wc_get_product() would otherwise fatal-error instead of failing gracefully.

6. Hands-on Exercise

7. Knowledge Check

Four quick questions. Expand each to check your answer.