TwinColumn Usage

I am working with an order management system. I have a composition relationship between my CustomerOrder entity and my OrderDetail entities. I also have a composition between CustomerOrder and Invoices. An Invoice also has a composition of InvoiceDetails. An InvoiceDetail has an association to the OrderDetail.

I want to be able to select the OrderDetails that I intend to generate an invoice for. I think that a TwinColumn component would work. If I can select the OrderDetails I want using the TwinColumn, and get a list of the selected OrderDetails from the right side, then I can loop over those OrderDetails and generate an InvoiceDetail for each of them and append it to the Invoice. Is it possible to get a list like that from the right side of the TwinColumn?

Right now, my right side is connected to a CollectionDatasource of OrderDetails. I’ve tried getItems() from that CollectionDatasource but it returns an empty list.