How to create mock data of STI in RSpec 【Ruby on Rails】

When your application has STI data, this method is necessary to test it.

Modal Structure

class Music
  # some codes

end

class Jazz < Music
  # some codes
  # this class has the "type" column and the value is "Jazz"

end

Factory

In this case, you might write codes like this.

FactoryBot.define do
  factory :music do
    title { Faker::Music.title }
  end

  trait :jazz do
    type 'Jazz'
  end
end

However, this codes are going to create the instance of music, not jazz

create :music, :jazz

You have to write tricky codes to solve this problem.

Solution

FactoryBot.define do
  factory :music do
    title { Faker::Music.title }
  end

  trait :jazz do
    type 'Jazz'
    initialize_with do
      klass = type.constantize
      klass.new(attributes)
    end
  end
end

It is necessary to use initialize_with.

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