Generate large file via Rails

Short: stream file - that's solution! :)

# lib/invoicescsvstreamer.rb

class InvoicesCsvStreamer

  def initialize
     @invoices = Invoices.all
  end

  def each
    yield csv_header
    @invoices.find_each do |invoice|
      yield csv_row(invoice)
    end
  end

  def csv_row(invoice)
    [invoice.uid, invoice.description, invoice.price, invoice.date].to_csv
  end

  def csv_header
    ["UID", "Description", "Price", "Date"].to_csv
  end
end

# app/controllers/invoices_controller.rb

class InvoicesController > ApplicationController
  def report
    @csv_streamer = InvoicesCsvStreamer.new
    response.headers["Last-Modified"] ||= Time.current
    self.response_body = @csv_streamer
  end
end