Code-Snippets-Functions/Execute a function on a child site/WooCommerce/add-specific-product-to-cart-together-with-the-main-product.txt

// Display checkbox(es) for additional product(s)
add_action('woocommerce_before_add_to_cart_button', 'display_additional_products_checkboxes');
function display_additional_products_checkboxes() {
    global $product;

    if ( $bundled_product_ids = $product->get_meta('_bundled_ids') ) {
        echo '<div class="additional-products">
        <h3>'. __('Additional Products') .'</h3>';

        foreach ($bundled_product_ids as $_product_id) {
            $_product = wc_get_product($_product_id);

            if ( is_object($_product) ) {
                printf('<div class="form-row"><label for="bundled-products-%d">
                <input type="checkbox" name="bundled_products[]" id="bundled-products-%d" value="%d">
                &nbsp;%s: %s</label></div>', 
                $_product_id, $_product_id, $_product_id, $_product->get_name(), $_product->get_price_html() );
            }
        }

        echo '</div><br>';
    }
}

// Add selected additional product IDs as custom cart item data
add_filter( 'woocommerce_add_cart_item_data', 'set_bundled_products_as_custom_item_data', 10 );
function set_bundled_products_as_custom_item_data( $cart_item_data ) {
    if ( ! isset($cart_item_data['parent_id']) 
    && isset($_POST['bundled_products']) && ! empty($_POST['bundled_products']) ) {
        $cart_item_data['bundled_products'] = wc_clean( wp_unslash($_POST['bundled_products']) );
    }
    return $cart_item_data;
}

// Add selected additional products as separated cart items
add_action( 'template_redirect', 'add_to_cart_bundled_products' );
function add_to_cart_bundled_products( $cart_item_data ) {
    if ( isset($_POST['bundled_products']) && ! empty($_POST['bundled_products']) ) {
        // Get the additional products
        $bundled_products = wc_clean( wp_unslash($_POST['bundled_products']) );

        // Get the parent bundle product ID
        $parent_id = isset($_POST['add-to-cart']) && $_POST['add-to-cart'] > 0 ? intval($_POST['add-to-cart']) : null;
        $parent_id = isset($_POST['variation_id']) && $_POST['variation_id'] > 0 ? intval($_POST['variation_id']) : $parent_id ;

        // Loop through additional selected product IDs
        foreach ( $bundled_products as $product_id ) {
            $product     = wc_get_product($product_id); // Get the product Object
            $is_variation = $product->is_type('variation'); // Is it a variation

            if ( is_object($product) ) {
                $variation_id = $is_variation ? $product_id : 0;
                $product_id = $is_variation ? $product->get_parent_id() : $product_id;
                $attributes = $is_variation ? $product->get_variation_attributes() : [];

                // Add additional product to cart (with the parent bundle product ID as custom cart item data)
                WC()->cart->add_to_cart($product_id, 1, $variation_id, $attributes, ['parent_id' => $parent_id ]);
            }
        }
    }
}