Never Fear, Traits are Here

I can’t count the number of times I’ve worked on Rails apps where I’m using Factory Girl and want to declare a factory with multiple parents. We’ve all been there, don’t lie.

    FactoryGirl.define do
      factory :user do
        name "Friendly User"

        factory :admin do
          admin true
        end

        factory :male_user do
          gender "Male"
          name   "John Doe"

          factory :male_admin_user do
            admin true
          end

          factory :teenage_male_user do
            date_of_birth { 15.years.ago }

            factory :teenage_admin_male_user do
              admin true
            end
          end
        end

        factory :female_user do
          gender "Female"
          name   "Jane Doe"

          factory :female_admin_user do
            admin true
          end

          factory :teenage_female_user do
            date_of_birth { 15.years.ago }

            factory :teenage_admin_female_user do
              admin true
            end
          end
        end
      end
    end

Oh, the duplication! This isn’t DRY.

Factory Girl 2.0.4 introduces traits. I’ll cut to the chase:

    FactoryGirl.define do
      factory :user do
        name "Friendly User"

        trait :admin do
          admin true
        end

        trait :male do
          gender "Male"
          name   "John Doe"
        end

        trait :female do
          gender "Female"
          name   "Jane Doe"
        end

        trait :teenager do
          date_of_birth { 15.years.ago }
        end

        factory :male_user,                 :traits => [:male]
        factory :female_user,               :traits => [:female]
        factory :teenage_male_user,         :traits => [:teenager, :male]
        factory :teenage_female_user,       :traits => [:teenager, :female]
        factory :male_admin_user,           :traits => [:admin, :male]
        factory :female_admin_user,         :traits => [:admin, :female]
        factory :teenage_admin_male_user,   :traits => [:teenager, :admin, :male]
        factory :teenage_admin_female_user, :traits => [:teenager, :admin, :female]
      end
    end

Mix and match however you please. Bonus: you can assign traits like plain-old attributes.

    FactoryGirl.define do
      factory :user do
        name "Friendly User"

        trait :admin do
          admin true
        end

        trait :male do
          gender "Male"
          name   "John Doe"
        end

        factory :male_admin_user do
          male
          admin
        end
      end
    end

Many props go out to Thomas Walpole, who helped get a lot of this written; thanks Thomas!

So go ahead, get your trait on; you’ll thank me later.

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