method_missing

With a factory definition block, you can use add_attribute, association, sequence, and trait to define a factory. You can also level a default method_missing definition for potential shortcuts.

Calling an unknown method (e.g. name, admin, email, account) connects an association, sequence, trait, or attribute to the factory:

1. If the method missing is passed a block, it always defines an attribute. This allows you to set the value for the attribute.

2. If the method missing is passed a hash as a argument with the key :factory, then it always defines an association. This allows you to override the factory used for the association.

3. If there is another factory of the same name, then it defines an association.

4. If there is a global sequence of the same name, then it defines an attribute with a value that pulls from the sequence.

5. If there is a trait of the same name for that factory, then it turns that trait on for all builds of this factory.

Using method_missing can turn an explicit definition:

FactoryBot.define do
  sequence(:email) { |n| "person#{n}@example.com" }
  factory :account
  factory :organization

  factory :user, traits: [:admin] do
    add_attribute(:name) { "Lord Nikon" }
    add_attribute(:email) { generate(:email) }
    association :account
    association :org, factory: :organization

    trait :admin do
      add_attribute(:admin) { true }
    end
  end
end

... into a more implicit definition:

FactoryBot.define do
  sequence(:email) { |n| "person#{n}@example.com" }
  factory :account
  factory :organization

  factory :user do
    name { "Lord Nikon" }      # no more `add_attribute`
    admin                      # no more :traits
    email                      # no more `add_attribute`
    account                    # no more `association`
    org factory: :organization # no more `association`

    trait :admin do
      admin { true }
    end
  end
end