Checkout with a single product: verify if ANY product is in the cart, and give error

Question

I can\'t imagine how to verify if the cart has some products inside, or not. I just need to allow ONE product for the checkout.

Here is the code used in class-wc-cart.p

Answer 1

Don't make changes directly in woocommerce core file because when you update plugin, might your code lost.

Add following code into functions.php and it will add only one product into cart:

add_filter( 'woocommerce_add_to_cart_validation', 'woocommerce_add_cart_item_data_custom' );

function woocommerce_add_cart_item_data_custom( $cart_item_data ) {

    global $woocommerce;
    if($woocommerce->cart->cart_contents_count > 0){
         wc_add_notice(
                     __( 'You cannot add another product to your cart.', 'woocommerce' ));

                return false;
    }
}