change columns on the fly by association

change csv values before import, find each author by 'Author name' and replace it with its id before insert

ActiveAdmin.register Post do
  active_admin_import validate: true,
                      headers_rewrites: { 'Author name': :author_id },
                      before_batch_import: ->(importer) {
                        authors_names = importer.values_at(:author_id)
                        # replacing author name with author id
                        authors   = Author.where(name: authors_names).pluck(:name, :id)
                        options = Hash[*authors.flatten] # #{"Jane" => 2, "John" => 1}
                        importer.batch_replace(:author_id, options)
                      }
end