Machinist vs Factory Girl: Machinist win!

Today I decided to verify if Machinist could be a good replacement for Factory Girl. In our project, we have a big problem with Factory Girl: even if you tell her not to hit the database, using the Factory.build method, if an object has associations, these are saved on the DB. And this causes a huge slowdown in specs using factories. We've been using Factory Girl for nearly two years, and if we could find a way to stop him hitting the DB, we could really have a huge improvent in our test suite running time.

To verify if Machinist could perform better, I set up a basic rails app. Look at this example:

	# person.rb
	validates_presence_of :address
	# person_factory.rb
	Factory.define :person do |p|
	p.name 'John'
	p.surname 'Doe'
	p.association :address
	end
	# person_spec.rb
	it "builds a valid person with factory girl" do
	Factory.build(:person).should be_valid
	end

view raw person_spec.rb hosted with ❤ by GitHub

If you do a tail -f log/test.log and you run this spec, you'll see something like this:

	AREL (0.5ms) INSERT INTO "addresses" ("country", "planet", "created_at",
	"updated_at") VALUES ('Italy', 'Earth', '2011-06-18 16:45:00.268423',
	'2011-06-18 16:45:00.268423')

view raw gistfile1.sql hosted with ❤ by GitHub

The Factory.build method has to save dependencies on the DB to set the foreign keys on the objects and validate them.

Let's try with machinist:

	# person.rb
	validates_presence_of :address
	# blueprints.rb
	Person.blueprint do
	name { "John" }
	surname { "Doe" }
	address { Address.make }
	end
	# person_spec.rb
	it "builds a valid person with machinist" do
	Person.make.should be_valid
	end

view raw person_spec.rb hosted with ❤ by GitHub

This time, running tail on the test.log file and running the spec, doesn't shown any DB hit, and of yeah, we have a green test.

I verified this also by putting a debugger line after the validation and inspecting the DB from within the debugger after the validation has run - with FactoryGirl, it revealed an Address object saved on the DB, while with Mechanist it didn't.

I still haven't looked inside machinist to show how it handles this, but I'll do it soon, so keep in touch!