Rails 3: How to respond_with csv without having a template file?

Question

I have an object that has a to_csv method and I want to pass it to respond_with to render csv from my controller. My code looks like this:

Answer 1

I've been struggling with the exact same problem. I might have found a solution.

I found some clues while reading the Renderers.add source code for :json and :xml (link is for Rails 3.0.10 code, 3.1 might have some changes already): https://github.com/rails/rails/blob/v3.0.10/actionpack/lib/action_controller/metal/renderers.rb

First, add a simple as_csv method to your model definition:

class Modelname < ActiveRecord::Base
  # ...
  def as_csv
    attributes
  end
end

This can be anything, just make sure to return a hash with key/value pairs. A Hash works better than an Array, as with keys you're able to add a header row to the CSV output later on. The idea for as_csv comes from Rails' as_json method, which return a Ruby object that is used by to_json to generate the actual JSON (text) output.

With the as_csv method in place, put the following code in a file in config/initializers inside your app (name it csv_renderer.rb, for example):

require 'csv' # adds a .to_csv method to Array instances

class Array 
  alias old_to_csv to_csv #keep reference to original to_csv method

  def to_csv(options = Hash.new)
    # override only if first element actually has as_csv method
    return old_to_csv(options) unless self.first.respond_to? :as_csv
    # use keys from first row as header columns
    out = first.as_csv.keys.to_csv(options)
    self.each { |r| out << r.as_csv.values.to_csv(options) }
    out
  end
end

ActionController::Renderers.add :csv do |csv, options|
  csv = csv.respond_to?(:to_csv) ? csv.to_csv() : csv
  self.content_type ||= Mime::CSV
  self.response_body = csv
end

And finally, add CSV support to your controller code:

class ModelnamesController < ApplicationController
  respond_to :html, :json, :csv

  def index
    @modelnames = Modelname.all
    respond_with(@modelnames)
  end

  # ...

end

The initializer code is largely based on the :json and :xml behaviour from the Rails source code (see link above).

Currently, the options hash passed to the block doesn't get passed to the to_csv call, as CSV is quite picky on which options it allows to be sent. Rails adds some default options by itself (like :template and some others), which gives you an error when passing them to to_csv. You can change the default CSV rendering behaviour by adding your own preferred CSV options to the initializer, of course.

Hope this helps!