How to specify traits for model associations in FactoryGirl

If you’re using RSpec and FactoryGirl to automate testing for your Rails app, you probably know that when creating a factory for a model that has association you can simply specify the factory of the associated model. For example, suppose your Contact model has associations with Phone and Store models:

FactoryGirl.define do factory :contact do |f| { } phone store end end

And you probably know you can have traits for factories, for example, different settings for different types of stores:

FactoryGirl.define do 
  factory :store do |f| 
    after(:create) { |store| 
      store.update_attributes :name => Faker::Name.last_name + " LLC" 

    trait :unknown do 
      after(:build) { |store| store.init_blank(Settings.feature_set_unknown) } 

    trait :restaurant do 
      after(:build) { |store| store.init_blank(Settings.feature_set_restaurant) } 

    trait :retailer do 
      after(:build) { |store| store.init_blank(Settings.feature_set_retailer) } 

However, what we could not find documented anywhere was how to specify a trait for an associations. Say when you create a contact factory you want specify which type of store that contact belongs to:

Here’s the magic decoder ring… use
:factory => [:association_factory_name, :trait_name]

FactoryGirl.define do 
  factory :contact do |f| { } 
    phone association :store, :factory => [:store, :unknown] 

    trait :foodie_contact do 
      association :store, :factory => [:store, :restaurant] 

    trait :retailer_contact do 
      association :store, :factory => [:store, :retailer] 

Which you can then invoke as follows in your examples:

c = FactoryGirl.create(:contact, :retailer_contact)

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