WooCommerce: Limit purchases to one product per order - php

Question

In WooCommerce I want to restrict the ordering of subscription products so that if one of them is added to the cart then you cannot add any other non-subscription products. The subscription products are in the array listed with their products ids.
The issue I have is that when a customer adds non-subscription products to the cart and then tries to add a subscription product the code works (as it should).
However, if they first add a subscription product and then try to add non-subscription products the code does not work and it allows all products in the cart.
This is the current code:
// If subscription box ordered limit cart to no other products
add_filter( 'woocommerce_add_to_cart_validation', 'wc_limit_one_per_order', 10, 2 );
function wc_limit_one_per_order( $passed_validation, $product_id ) {
if ( ! in_array( $product_id, array( 245632, 245626, 245623, 245620, 245617, 245614, 245610, 245606, 245601 ) ) ) {
return $passed_validation;
}
if ( WC()->cart->get_cart_contents_count() >= 1 ) {
wc_add_notice( __( 'The subscription box cannot be purchased with other non-subscripton box products. Please, empty your cart first and then add it again.', 'woocommerce' ), 'error' );
return false;
}
return $passed_validation;
}

Answer 1

What are you missing, and you can include this in your function, is to check the cart for its contents. You'll need to loop over the cart items, and review the possibilities. I outlined it below
Firstly check the cart for existing products with subscriptions
Then check what is being added ($product_id). If a subscription exists, and another subscription is added. I guess there is no problem?
After that, you want respond to when a non-subscription product is added while the cart has a subscription product
And lastly, in the final else statement, it's possible to check the alternative: When a non-subscription product is in the cart and a subscription product is added.
Anyway, there might be some mistakes in the code, also with validation parameter. I didn't take that into account. Also, it can easily be simplified. Just wanted to outline all possibilities.
$subscription_products = array( 245632, 245626, 245623, 245620, 245617, 245614, 245610, 245606, 245601 );
foreach (WC()->cart->get_cart() as $cart_item_key => $values) {
$_product = $values['data'];
// is there a subscription in the cart?
if( in_array($_product->get_id(), $subscription_products) ) {
// yes!
// are we adding a subscription product?
if( in_array($product_id, $subscription_products) ) {
// we are. All good.
} else {
// no we are not. We can decide to empty the cart
unset(WC()->cart->cart_contents[$cart_item_key]);
wc_add_notice( 'Custom error message', 'error' );
// OR not add the product (return false)
return false;
}
//
} else {
// no!
// are we adding a subscription product?
if( in_array($product_id, $subscription_products) ) {
// we are. A Problem!
// We can decide to empty the cart
unset(WC()->cart->cart_contents[$cart_item_key]);
wc_add_notice( 'Custom error message', 'error' );
// OR not add the product (return false)
return false;
}
}
}