create embedded record on existing record

create embedded record on existing record

yo. Thanks to a response here, I figured out how to create embedded child
records along with a newly created parent. However, I've been unable to
add the embedded record to an existing parent.
I've tried using setupcontroller to get the content of my parent model
into the appropriate child route/controller, but i I'm still unable to
retrieve the loaded parent.
this. get controllers . post brings up the record as undefined. How do I
get the content of the parent loaded in order to add child records to it?