class PopulateEditionsPart1 < ActiveRecord::Migration[5.0]
  disable_ddl_transaction!

  def up
    execute "UPDATE content_items SET document_id = (
               SELECT id FROM documents
               WHERE documents.content_id = content_items.content_id AND
                  documents.locale = content_items.locale
             )"
  end
end

class PopulateEditionsPart1 < ActiveRecord::Migration[5.0]
  def up
    Document.find_each do |doc|
        ContentItem.where(content_id: doc.content_id, locale: doc.locale)
            .update_all(document_id: doc.id)
    end
  end
end

Switch to a migration that uses ActiveRecord
Switch to a migration that uses ActiveRecord
