seeds.rb

class Seed
  @ids = {}
  @classes = {}

  def self.create(factory_name, attributes = nil)
    raise "attributes must be a hash" if attributes && !attributes.is_a?(Hash)

    model = FactoryGirl.create(factory_name, attributes)
    @ids[factory_name] = model.id
    @classes[factory_name] = model.class

    model
  end

  def self.[](factory_name)
    seed_id = @ids[factory_name]

    if seed_id
      seed_class = @classes[factory_name]
      seed_class.find_by_id(seed_id) || create(factory_name)
    else
      create(factory_name)
    end
  end
end

def seed(factory_name)
  Seed[factory_name]
end