php - Prevent add to cart if cart contains a specific Woocommerce product category

Question

My question and code is directly based off of this question - " I have a store containing 5 categories. It's multivendor and due to shipping complications, I can only sell products from one specific category ('paint') when they are alone in the cart. So I need to prevent add to cart of any non-paint products when the cart contains paint, and display an error message, and I need to prevent paint products being added to a cart containing any other categories, and disaply an error message.

I've tried to cobble together this code from snippets I've found lying around on Stackoverflow and elsewhere. The logic seems to work in my brain, but when I try to implement the code (through functions.php) it prevents any product from being added to the cart unless the cart is empty."

Link to question - Prevent add to cart if cart contains a specific category (WooCommerce)

I have checked and modified the accepted answer to suit my needs however it doesnt seem to work at all as i have the same question just related to a different category (ie gas instead of paint), it was my understanding that I would just have to modify the "has_term" function in order to get this to work as it is just a matter of pointing to a particular category?

//*** Prevent mixture of gas and other prods in same cart ***//
function dont_add_gas_to_cart_containing_other($validation, $product_id) {

// Set flag false until we find a product in gas
    $cart_has_gas = false;

// Set $cat_check true if a cart item is in gas cat
    foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item) {

        $product = $cart_item['data'];

        if (has_term('Gas', 'Gas Tanks & Accessories', $product->id)) {
            $cart_has_gas = true;
            // break because we only need one "true" to matter here
            break;
        }
    }

    $product_is_gas = false;
    if (has_term('Gas', 'Gas Tanks & Accessories', $product_id)) {
        $product_is_gas = true;
    }

// Return true if cart empty
    if (!WC()->cart->get_cart_contents_count() == 0) {
        // If cart contains gas and product to be added is not gas, display error message and return false.
        if ($cart_has_gas && !$product_is_gas) {
            wc_add_notice('Sorry, you can only purchase Helium Gas products on their own. To purchase this product, please checkout your current cart or empty your cart and try again', 'error');
            $validation = false;
        }
        // If cart contains a product that is not gas and product to be added is gas, display error message and return false.
        elseif (!$cart_has_gas && $product_is_gas) {
            wc_add_notice('Sorry, you can only purchase Helium Gas products on their own. To purchase this product, please checkout your current cart or empty your cart and try again', 'error');
            $validation = false;
        }
    }
    // Otherwise, return true.
    return $validation;
}

add_filter('woocommerce_add_to_cart_validation', 'dont_add_gas_to_cart_containing_other', 10, 2);

question from:https://stackoverflow.com/questions/65918488/prevent-add-to-cart-if-cart-contains-a-specific-woocommerce-product-category

Answer 1

Because you gave the category name to the function, you must give the function a slug, second parameter should be 'product_cat' and last parameter should be a Product ID.

$product = $cart_item['data'];

if( has_term( 'gas', 'product_cat', $product->get_id() ) ) {
    ......
}