如何在ruby datamapper中设置一个属性是同一对象的另一个属性的函数？

class User
  include DataMapper::Resource
  
  property :id, Serial
  property :name, String
  property :age, Integer
end

class Profile
  include DataMapper::Resource
  
  property :id, Serial
  property :bio, Text
  
  belongs_to :user
end

class User
  include DataMapper::Resource
  
  property :id, Serial
  property :name, String
  property :age, Integer
  
  belongs_to :profile, 'Profile', required: false
  
  def bio
    profile.bio if profile
  end
  
  def bio=(new_bio)
    self.profile ||= Profile.new
    self.profile.bio = new_bio
  end
end