exporter.rb

require 'csv'

class Exporter
  DEFAULT_EXPORT_TABLES = [ Invoice, InvoiceItem, Item, Merchant, Transaction, User ]
  DESTINATION_FOLDER = "tmp/"

  def self.export_tables_to_csv(tables = DEFAULT_EXPORT_TABLES)
    tables.each { |klass| export_table_to_csv(klass) }
  end

  def self.export_table_to_csv(klass)
    output_file = CSV.open(filename_for_class(klass), "w")
    output_file << klass.headers
    klass.data.each{ |row| output_file << row }
    output_file.close
  end

  def self.filename_for_class(klass)
    DESTINATION_FOLDER + klass.to_s.underscore + '.csv'
  end
end

class ActiveRecord::Base
  def self.data
    find(:all).map{ |i| i.data}
  end
  
  def self.headers
    columns.map(&:name)
  end
  
  def data
    self.class.headers.map { |column| self.send(column) }
  end
end