Simple Exporter

exporter.rb

require 'csv'

# Class that takes a set of records from a Rails app and returns CSV'd goodness
# Record's must implement class method #csv_exportable_headers and instance method #csv_exportable_attributes
# Note: This probably should be moved to a module where the headers / attributes are defined
class Exporter
  module CSV
    def self.export(records)
      # TODO: dropout if records is blank
      klass = records.model_name.constantize
      raise "#{klass} must implement csv_exportable_headers"    unless klass.respond_to? :csv_exportable_headers
      raise "#{klass} must implement csv_exportable_attributes" unless klass.method_defined? :csv_exportable_attributes
      ::CSV.generate do |csv|
        # headers
        csv << klass.csv_exportable_headers
        # values
        records.each do |record|
          csv << record.csv_exportable_attributes
        end
      end
    end
  end
end

### TESTS ###

require 'spec_helper'

class Item
  def attribute_a
    'Attribute A value'
  end

  def attribute_b
    'Attribute B value'
  end
end

describe Exporter do
  context 'csv' do
    describe 'self.export' do
      it 'should raise an error if passed record model does not implement #csv_exportable_headers' do
        lambda { Exporter::CSV.export(Item.new) }.should raise_error, 'Item must implement csv_exportable_headers'
      end

      it 'should raise an error if passed records does not implement #csv_exportable_attributes' do
        Item.instance_eval { def csv_exportable_headers; end }
        lambda { Exporter::CSV.export(Item.new) }.should raise_error, 'Item must implement csv_exportable_attributes'
      end

      it 'should help me' do
        Item.instance_eval { def csv_exportable_headers; ["Attribute A", "Attribute B"]; end }
        Item.class_eval    { def csv_exportable_attributes; [:attribute_a, :attribute_b]; end }
        # As this is a rails app, Exporter expects an ActiveRecord::Relation
        # which responds to #model_name. Give it what it wants.
        fake_active_record_relation = [Item.new]
        fake_active_record_relation.stub(:model_name => 'Item')
        Exporter::CSV.export(fake_active_record_relation).should == "Attribute A,Attribute B\nattribute_a,attribute_b\n"
      end
    end
  end
end