How do I redirect to the cart page if I click on the 'Add to cart' button for a product that's already in cart

Question

How do I redirect to the cart page if I click on the 'Add to cart' button for a product that's already in cart?

Woocommerce/wordpress:

This is my code currently. At the moment it is not redirecting to the cart page.

    add_filter( 'woocommerce_add_to_cart_redirect', 'woo_in_cart' );
function woo_in_cart($product_id) {
    global $woocommerce;         
    $url = WC()->cart->get_cart_url();
    foreach($woocommerce->cart->get_cart() as $key => $val ) {
        $_product = $val['data'];

        if($product_id == $_product->id ) {
            wp_redirect($url);
        }
    }         
}

Answer 1

this snippet does what you asked for, and it supports ajax calls. some points about with your code:

1- 'woocommerce_add_to_cart_redirect' fires when product is already added to cart.

2- WC()->cart->get_cart_url() is deprecated

3- will not redirect if ajax add to cart is enabled

add_filter('woocommerce_add_to_cart_validation' , 'shalior_flag_already_added_products_as_invalid' , 10 , 2);
function shalior_flag_already_added_products_as_invalid ($result , $product_id){
    if (false === $result){
        return $result;
    }

    $url = wc_get_cart_url();
    foreach ( WC()->cart->get_cart() as $cart_item ) {
        $cart_item_product_id = $cart_item['product_id'];
        if($product_id === $cart_item['product_id'] ) {
            $result = false;
        }
    }
    if (false === $result){
        add_filter('woocommerce_cart_redirect_after_error' , function (){
            return wc_get_cart_url();
        } , 999 );
    }
    return $result;
}