Export CSV with Mongoid and FasterCSV - ruby-on-rails

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.