reports_controller.rb

  def costs
    startdate = Date.parse(params[:startdate])
    enddate = Date.parse(params[:enddate])

    respond_to do |format|
      format.csv do
        headers['X-Accel-Buffering'] = 'no' # Stop NGINX from buffering
        headers["Cache-Control"] = "no-cache" # Stop downstream caching
        headers["Transfer-Encoding"] = "chunked" # Chunked response header
        headers.delete("Content-Length") # See one line above
        headers["Content-Disposition"] = %(attachment; filename="export.csv")

        self.response_body = Enumerator.new do |lines|
          lines << ['date', 'property_id', 'channel_id', 'Amount EUR', 'Amount Hotel Currency', 'Hotel Currency'].join(',').to_s
          ArCost.includes(:property).where(report_date: startdate..enddate).find_each do |cost|
            lines << [cost.report_date, cost.property.property_id, cost.channel_id, cost.channel_cost_eur, cost.channel_cost_hotel_currency, cost.hotel_currency].join(',').to_s
          end
        end

      end 
    end

  end