How to make a has_one associated model show up in class attributes() result?

Question

Where Person has_one Brain, should I expect brain to show up in the hash returned by attributes() for Person? If so, how to make that happen?

Rails Console output:

1.9.3p327 :003 > Person.new.attributes
 => {"id"=>nil, "name"=>nil, "created_at"=>nil, "updated_at"=>nil} 
1.9.3p327 :004 > Brain.new.attributes
 => {"id"=>nil, "weight_kg"=>nil, "created_at"=>nil, "updated_at"=>nil, "person_id"=>nil} 

The two models are Person and Brain:

class Person < ActiveRecord::Base
  has_one :brain
  attr_accessible :name
  attr_accessible :brain
  attr_accessible :brain_attributes
  accepts_nested_attributes_for :brain

end

class Brain < ActiveRecord::Base
  belongs_to :person
  attr_accessible :weight_kg
  attr_accessible :person
  attr_accessible :person_attributes
  accepts_nested_attributes_for :person
end

person_id shows up in the attributes for Brain because the brains table has a person_id column. No such column need exist for the people table.

Answer 1

not sure it is a good idea to list associations among attributes, but you can get association names like this:

association_names = self.class.reflect_on_all_associations.map(&:name)

see doc on reflections

Answer 2

It doesn't show attributes for brain in person because if you look at the sql table for person .. there is no field for "brain" .. but in the brain table there is person_id.

Good tip from Viktor on how to reflect on associations!