Returning CSV data to the browser

March 23rd, 2006

Over on the Rails mailing list, Pete asks:

One of my apps has to export data for the backend system to process it. What’s the best way to create a CSV file in Rails and then return it as a file to the client?

I have used two tricks in the past to export the data.

Exporting using CSV::Writer

This is simple. Use CSV::Writer and ActionController’s send_data method.

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class ReportController < ApplicationController
  def report
    @models = Model.find(:all, :conditions => ['...'])
    report = StringIO.new
    CSV::Writer.generate(report, ',') do |csv|
      csv << %w(Title Total)
      @models.each do |model|
        csv << [model.title, model.total]
      end
    end

    report.rewind
    send_data(report.read,
      :type => 'text/csv; charset=iso-8859-1; header=present',
      :filename => 'report.csv')
  end
end

By default, send_data will make the Content-Disposition header equal to attachment. This will ask the browser to download the file, instead of displaying it in the browser window.

Exporting using a regular view

The second method is even simpler:

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class ReportController < ApplicationController
  def report
    @models = Model.find(:all, :conditions => ['...'])
    response.headers['Content-Type'] = 'text/csv; charset=iso-8859-1; header=present'
    response.headers['Content-Disposition'] = 'attachment; filename=report.csv'
  end
end
 
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Title,Value
<% @models.each do |model| -%>
"<%= model.title.gsub('"', '""') %>",<%= model.value %>
<% end -%>

Notice how I escape quotes in the view ? This is important, or else your parsing will be broken when you read the file back in. Of course, if you use CSV::Writer, you won’t have to muck with that – it will all be taken care of for you.

UPDATE 2006-03-30: Changed Content-Type from text/comma-separated-values to text/csv, and added the header optional parameter, per RFC 4180

UPDATE 2007-04-26: Just noticed that the report method above would render with a layout if one were defined in ApplicationController. Simply call #render and tell it to use no layout: render :action => :report, :layout => false

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I am François Beausoleil, a Ruby on Rails coder. During the day, I work on XLsuite. At night, I am interested many things. Read my biography

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