I am still fairly new to SaleforceDX. I have been tasked with putting together a sample data plan matching a small portion of our production data, for our new Scratch-Orgs. With foreign-key type relationships, I am having no problems whatsoever (Using the '@' symbol to build references like @AccountRef1). However, I am failing to see how this would be done when there isn't such a foreign-key type of field (master-detail and __r relationships specifically.) I have read a bit about putting together embedded queries, but that seems like it could get ugly, and I don't completely understand it. My question is: how do I import related objects without a field to put the @ related object reference into?
For example: A relates to B. How do I specify a relationship like B.ClassOfA.Id='@RefId' in my Plan's JSON file for B.