Automatically add product to cart when visiting single product page in WooCommerce

Question

So i need to get the product auto added to cart if the user visits the product page so like this

add_action( 'template_redirect', 'add_product_to_cart' );
function add_product_to_cart() {
    global $product;

    if ( ! is_admin() ) {
        $product_id = 13;
        $found = false;
        //check if product already in cart
        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 )
                    $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 );
        }
    }
}

---

This works great but what i need to is to do this for any visited product so modified the code to get the current product ID like this

add_action( 'template_redirect', 'add_product_to_cart' );
function add_product_to_cart() {
    global $product;
    if ( ! is_admin() ) {
        $product_id = $product->get_id();
        $found = false;
        //check if product already in cart
        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 )
                    $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 );
        }
    }
}

But when doing that i get this error:

Uncaught Error: Call to a member function get_id() on null. How to go about this?

Answer 1

The error will occur when $product is not known. This is because the template_redirect hook is not only executed on the single product page. So it's better to use a hook like woocommerce_single_product_summary

So you get:

function action_woocommerce_single_product_summary() {
    // Get the global product object
    global $product;
    
    // Quantity for add to cart
    $quantity = 1;
    
    // Is a WC product
    if ( is_a( $product, 'WC_Product' ) ) {
        // Get ID
        $product_id = $product->get_id();
        
        // WC Cart
        if ( WC()->cart ) {
            // Get cart
            $cart = WC()->cart;
            
            // Cart NOT empty
            if ( sizeof( $cart->get_cart() ) > 0 ) {
                // Cart id
                $product_cart_id = $cart->generate_cart_id( $product_id );
            
                // Find product in cart
                $in_cart = $cart->find_product_in_cart( $product_cart_id );
                
                // NOT in cart
                if ( ! $in_cart ) {
                    $cart->add_to_cart( $product_id, $quantity );
                }
            } else {
                $cart->add_to_cart( $product_id, $quantity );          
            }
        }
    }
}
add_action( 'woocommerce_single_product_summary', 'action_woocommerce_single_product_summary', 10, 0 );