How to add Id as a default value to a field when its' model is not the context model

On the mobile builder I have an object for Orders and a button that creates a new Order and all of the detail required.

I then have a product grid view and a button within this that adds a new “Order Item” record, allows entry of quantity etc and inserts the Product Id as a default field

Inserting the Product Id as a default field value is ok as the button sits within the context of the Product model but I also need to add the Order Id to the Order Item record to ensure that the Order Item is attached to the Order as a child but for the life of me I cant find how to find the Order Id given the button isnt within the Order model context.

I have tried every combination of {{Orders__r.Id}} I can think of and I am not familiar with writing snippets to achieve this?

Is there a simple way as it sounds simple to me )