Easy example, CPTs for Books and Book Authors. I want multiple authors on each book. I've read, and verified, that the multiple select relationship fields create serialized data in wp_podsrel.
What are my options? Is importing serialized data straightforward, so if I could possibly figure out the correct post_ids for each book author, I could put that data in a field is a CSV file?
I know that it was suggested in that post to use add_to, but I am not sure what that does, so I could use some guidance there (I normally work my way back from the examples).