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

If you run 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')

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

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 stay tuned!