Woocommerce, Get Current Product Id

2017 Update - since WooCommerce 3:

global $product;
$id = $product->get_id();

Woocommerce doesn't like you accessing those variables directly. This will get rid of any warnings from woocommerce if your wp_debug is true.

If the query hasn't been modified by a plugin for some reason, you should be able to get a single product page's "id" via

global $post;
$id = $post->ID

OR

global $product;
$id = $product->id;

EDIT: As of WooCommerce 3.0 this needs to be

global $product;
$id = $product->get_id();

Since WooCommerce 2.2 you are able to simply use the wc_get_product Method. As an argument you can pass the ID or simply leave it empty if you're already in the loop.

wc_get_product()->get_id();

OR with 2 lines

$product = wc_get_product();
$id = $product->get_id();

Retrieve the ID of the current item in the WordPress Loop.

echo get_the_ID(); 

hence works for the product id too. #tested #woo-commerce

The correct method is:

global $product;

$id = $product->get_id();

Save the current product id before entering your loop:

$current_product = $product->id;

Then in your loop for your sidebar, use $product->id again to compare:

 <li><a <? if ($product->id == $current_product) { echo "class='on'"; }?> href="<?=get_permalink();?>"><?=the_title();?></a></li>

your can query woocommerce programatically you can even add a product to your shopping cart. I'm sure you can figure out how to interact with woocommerce cart once you read the code. how to interact with woocommerce cart programatically

====================================

<?php

add_action('wp_loaded', 'add_product_to_cart');
function add_product_to_cart()
{
    global $wpdb;

    if (!is_admin()) {


        $product_id = wc_get_product_id_by_sku('L3-670115');

        $found = false;

        if (is_user_logged_in()) {
            if (sizeof(WC()->cart->get_cart()) > 0) {
                foreach (WC()->cart->get_cart() as $cart_item_key => $values) {
                    $_product = $values['data'];
                    if ($_product->get_id() == $product_id)
                        WC()->cart->remove_cart_item($cart_item_key);
                }
            }
        } else {
            if (sizeof(WC()->cart->get_cart()) > 0) {
                foreach (WC()->cart->get_cart() as $cart_item_key => $values) {
                    $_product = $values['data'];
                    if ($_product->id == $product_id)
                        $found = true;
                }
                // if product not found, add it
                if (!$found)
                    WC()->cart->add_to_cart($product_id);
            } else {
                // if no products in cart, add it
                WC()->cart->add_to_cart($product_id);
            }
        }
    }
}