I wanted to create a factory that would link various states to my model, but from a specified list instead of automatically generated. I discovered that these are transient attributes:

FactoryGirl.define do
  factory :business do
    name "MyString"
#
#
#
    trait :with_states do
      ignore do
        state_list []
      end
      # add association equal to state code
      after(:create) do |business, evaluator|
        evaluator.state_list.each do |state_code|
          business.states << State.find_by(state_code: state_code)
        end
      end
    end
  end
end

This factory can now be called with:

  FactoryGirl.create(:business, :with_states. state_list: %w(KY IN))

Of course, now that I’m passing in the attributes, I can probably just use:

FactoryGirl.define do
  factory :business do
    name "MyString"
#
#
#
    ignore do
      with_states []
    end
    # add association equal to state code
    after(:create) do |business, evaluator|
      evaluator.with_states.each do |state_code|
        business.states << State.find_by(state_code: state_code)
      end
    end
  end
end

and then the call is even simpler:

  FactoryGirl.create(:business, with_states: %w(KY IN))