Allow only one product category in cart at once in Woocommerce

Question

How would I go about configuring the Woocommerce cart to only allow one product category type in it at a time?

Answer 1

The following code will allow adding to cart only items from one product category avoiding add to cart and displaying a custom notice:

add_filter( 'woocommerce_add_to_cart_validation', 'only_one_product_category_allowed', 20, 3 );
function only_one_product_category_allowed( $passed, $product_id, $quantity) {

    // Getting the product categories term slugs in an array for the current product
    $term_slugs   = wp_get_post_terms( $product_id, 'product_cat', array('fields' => 'slugs') );

    // Loop through cart items
    foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item ){

        // Check if the product category of the current product don't match with a cart item
        if( ! has_term( $term_slugs, 'product_cat', $cart_item['product_id'] ) ){

            // Displaying a custom notice
            wc_add_notice( __('Only items from one product category are allowed in cart'), 'error' );

            // Avoid add to cart
            return false; // exit
        }
    }
    return $passed;
}

Code goes in function.php file of the active child theme (or active theme). Tested and works.

---

Addition (updated) - The same but only for parent product categories:

add_filter( 'woocommerce_add_to_cart_validation', 'only_one_product_category_allowed', 20, 3 );
function only_one_product_category_allowed( $passed, $product_id, $quantity) {
    $parent_term_ids = $item_parent_term_ids = array(); // Initializing

    // Loop through the current product category terms to get only parent main category term
    foreach( get_the_terms( $product_id, 'product_cat' ) as $term ){
        if( $term->parent > 0 ){
            $parent_term_ids[] = $term->parent; // Set the parent product category
        }
    }

    // Loop through cart items
    foreach (WC()->cart->get_cart() as $cart_item_key => $cart_item ){
        // Loop through the cart item product category terms to get only parent main category term
        foreach( get_the_terms( $cart_item['product_id'], 'product_cat' ) as $term ){
            if( $term->parent > 0 ){
                $item_parent_term_ids[] = $term->parent; // Set the parent product category
            }
        }

        // Check if parent product categories don't match
        if( ! array_intersect( $parent_term_ids, $item_parent_term_ids ) ){

            // Displaying a custom notice
            wc_add_notice( __('Only items from one product category are allowed in cart'), 'error' );

            // Avoid add to cart
            return false; // exit
        }
    }
    return $passed;
}

Code goes in function.php file of the active child theme (or active theme). Tested and works.