How to implement the “pre-order” functionality in an online store (on CMS Bitrix or UMI)?

Question

CMS

When developing an online store, such a question arose. A very common and standard situation is when a product listed in the catalog is currently out of stock. On our handwritten site, we implemented an order for such a product in the following way: for such a product, instead of the "buy" or "add to cart" button, the "pre-order" button was displayed. Those. such a product is added to the cart as "pre-order" (it may even have no price) and when a customer places such an order, it appears in the order database with the status "pre-order". Those. the client has placed such an order and is waiting for a notification when the product becomes available and he will be notified about it. Everything would be fine, but it is possible that the client added to the cart an item that is in stock and an item that is not available. In this case, such an order cannot be marked with the status "pre-order", because it also contains goods that are in stock and can already be sent to the client. In this case, our system acted as follows: the order was simply automatically split into two orders - in one, the goods (s) that were in stock remained, in the other - pre-order.
The question arises how this is implemented in popular CMS systems and is it implemented at all? Those. Is there such a thing as "preorder"? Maybe there is a possibility of manual splitting of the order by the manager into an order that has a pre-order product and an order that does not?

Answer 1

In Bitrix there is a checkbox "Allow subscription in the absence of goods" - the client will receive a notification by mail when the goods are available. Or checkbox "Allow purchase in the absence of goods" - the client will be able to put in the basket the goods that are physically absent in the warehouse, and the seller himself will decide how to sell it to the client.
Shipment of orders is possible with a breakdown into several deliveries / shipments.