Bryan Helmkamp

For a recent “enterprisey” project I’m working on, we had to offer a variety of CSV exports for many of the models in our system. Ruby’s FasterCSV library is great for raw parsing and generation of CSV data, so I used that as the basis for a quick and dirty system to easily provide customizable exports.

The main features are:

• Transform an array of exportable records into a whole CSV file. (By default, FasterCSV transforms arrays into a single CSV row.)
• Export a whole table my calling .to_csv on the ActiveRecord subclass.
• By default, export all of an ActiveRecord’s columns except for created_at and updated_at.
• Allow simple customization of exportable columns by overriding the export_columns method in your ActiveRecord class.
• Allow multiple CSV formats by conditionally branching inside the export_columns method depending on the format parameter.
• Allow complete customization of the export by overriding the to_row method. (I haven’t actually needed this much customization yet.)

The simplest example:

Address.to_csv

Customizing the columns included in the CSV:

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class Address < ActiveRecord::Base
  def export_columns(format = nil)
    %w[city state postal_code]
  end
end

Multiple output formats:

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class Address < ActiveRecord::Base
  def export_columns(format = nil)
    case format
    when :local
      %w[street1 street2 city state postal_code]
    else
      %w[city state postal_code]
    end
  end
end

Here’s the code:

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require "fastercsv"

class ActiveRecord::Base
  def self.to_csv(*args)
    find(:all).to_csv(*args)
  end
  
  def export_columns(format = nil)
    self.class.content_columns.map(&:name) - ['created_at', 'updated_at']
  end
  
  def to_row(format = nil)
    export_columns(format).map { |c| self.send(c) }
  end
end

class Array
  def to_csv(options = {})
    if all? { |e| e.respond_to?(:to_row) }
      header_row = first.export_columns(options[:format]).to_csv
      content_rows = map { |e| e.to_row(options[:format]) }.map(&:to_csv)
      ([header_row] + content_rows).join
    else
      FasterCSV.generate_line(self, options)
    end
  end
end