listings_controller.rb

    if params[:map_listing][:file]
      file_field = params[:map_listing][:file]
      session[:map_fields] = {}
      temp_path = File.join(Dir::tmpdir, "map_fields_#{Time.now.to_i}_#{$$}")
      File.open(temp_path, 'wb') do |f|
        f.write file_field.read
      end
      session[:map_fields][:file] = temp_path
    end
    CSV.foreach(session[:map_fields][:file], { :headers => true, :return_headers => true }) do |row|
      @import_headers = row if row.header_row?
    end