I have a nested field called released with three values
A node can have multiple releases. However, in the old dataset (d7), each node only had one release and the fields just a part of the node.
I want to now migrate it to the new format in d8
If it was just one value, I could do this
released/by: field_released_by released/when: field_released_at
I tried the solution at https://www.freelock.com/blog/john-locke/2017-12/slick-migration-trick-convert-columns-multi-value-field-subfields which didn't help. It tried to look up the dummy fields and caused it to fail.
I can't be the first person to come across this requirement so I am loathe to write a process plugin for it.
Is there a straightforward solution for this? or is a process plugin the only way?