Question

Class UserController
  def export_users
    users = User.all
    stream_csv do |csv|
      csv << ["Name","Email","Gender"]
      users.each do |i|
        csv << [i.name,i.email,i.gender]
      end
    end
  end

def stream_csv
    require 'fastercsv'

        filename = params[:action] + ".csv"

        #this is required if you want this to work with IE      
        if request.env['HTTP_USER_AGENT'] =~ /msie/i
            headers['Pragma'] = 'public'
            headers["Content-type"] = "text/plain"
            headers['Cache-Control'] = 'no-cache, must-revalidate, post-check=0, pre-check=0'
            headers['Content-Disposition'] = "attachment; filename=\"#{filename}\""
            headers['Expires'] = "0"
        else
            headers["Content-Type"] ||= 'text/csv'
            headers["Content-Disposition"] = "attachment; filename=\"#{filename}\""
            controller.response.headers["Content-Transfer-Encoding"] = "binary"
        end

        render :text => Proc.new { |response, output|
            csv = FasterCSV.new(output, :row_sep => "\r\n")
            yield csv
        }
    end
end

Err: “#Proc:0x9382539@/sites/app/controllers/export_controller.rb:56”

Using Ruby 1.8 and Rails 3.0.9

So I think the problem here is that I’m not using “Proc” right. Or it’s not supposed to act like just another block…

I thought about programming a new logic into the class so that reads better. But if somebody could explain to me why my code is wrong or at least point me in a new direction than I might be able to learn something new here. Thanks

Note: Found a better way:

def export_inverts
  require 'fastercsv'
  inverts = Invert.all
  filename = params[:action] + ".csv"

  #this is required if you want this to work with IE
  if request.env['HTTP_USER_AGENT'] =~ /msie/i
    headers['Pragma'] = 'public'
    headers["Content-type"] = "text/plain"
    headers['Cache-Control'] = 'no-cache, must-revalidate, post-check=0, pre-check=0'
    headers['Content-Disposition'] = "attachment; filename=\"#{filename}\""
    headers['Expires'] = "0"
  else
    headers["Content-Type"] ||= 'text/csv'
    headers["Content-Disposition"] = "attachment; filename=\"#{filename}\""
    headers["Content-Transfer-Encoding"] = "binary"
  end

  csv_string = FasterCSV.generate do |csv|
    csv << ["Genus","Species","Common Name","Pet Name","Gender"]
    inverts.each do |i|
      csv << [i.scientific_name,i.scientific_name,i.common_name,i.pet_name,i.gender]
    end
  end
  render :text => csv_string
end

Answer 1

Yield can only be used inside a function or a block. Yield is used in a function that takes a block to say, yield some value into the block. Actually it says yield this value into the proc that the block has been converted into with the ampersand operator (in most cases). However, you could pass a Proc to a function that was expecting it.

Here, you just want to return the value from the proc and “yield” isn’t needed.