with_archive.rb

module WithArchive
  def with_archive
    columns         = column_names
    archive_class   = const_get(:Archive)
    archive_columns = columns.map { |c| c == 'state' ? "'disabled' AS state" : c }
    from <<-sql
      (#{unscoped.select(columns.join(', ')).to_sql}
       UNION
       #{archive_class.unscoped.select(archive_columns.join(', ')).to_sql}
      ) as #{table_name}
    sql
  end
end