通过accepts_nested_attributes_for保存时，虚拟属性为nil

Question

When I save a record through nested attributes, the virtual attribute doesn't get set in the child model.

class Person < ActiveRecord::Base
  has_many :houses
  accepts_nested_attributes_for :houses
end

class House < ActiveRecord::Base
  attr_accessor :house_name  #virtual
  before_save do 
    puts attributes # doesn't include house_name when saving through parent model
    puts @house_name # nil when saving through parent model
  end

end

person = Person.find(1)
person.houses.count #=> 3
person.houses.first.house_name = 'crazy house'
person.save # house_name not in attributes

house = person.houses.first
house.house_name = 'moms house'
house.save #house_name is in attributes

Answer 1

Your code:

person.houses.first.house_name = 'crazy house'

fetches the first associated House . Person has no way to know if you change it's house. You just overestimated the magic, I guess. All you need is to update_attributes of the house:

person.houses.first.update_attributes house_name: 'crazy house'