I hope its not a stupid question...
...but what is the best way to store a custom product_attribute (it's simply setup via admin backend) to the order and invoice to make it persistent and not dependant from the current product setup?
Reason: I want to get this value from the "$invoice->getAllItems()" later on to create an xls/export for my purpose with the data from the moment the order was done.
It seems only the custom options are stored persistent in the order after checkout?
thanks for you help,