WARNING: Can't mass-assign protected attributes

I get this error "WARNING: Can't mass-assign protected attributes: races_attributes" , when following this http://railscasts.com/episodes/196-nested-model-form-part-1 on rails 3.

Where Races are a component of Events. This is my models/race.rb:

class Race < ActiveRecord::Base
belongs_to :event

attr_accessible :name, :unit
end

This is my models/event.rb:

class Event < ActiveRecord::Base
has_many :races, :dependent => :destroy

accepts_nested_attributes_for :races

attr_accessible :name, :date, :description, :location_name, :address_one, :addres开发者_运维技巧s_two, :city, :state, :zip, :active, :races_attributes
end

Any Ideas?

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Shorter than using attr_accessible, safer than using whitelist_attributes: attr_protected

Just indicate the protected attributes, and Rails will infer that all others can be mass-assigned:

class MyClass < ActiveRecord::Base
  attr_protected :id
end

(I always have way more attributes that I want mass-assigned than the ones I want protected.)

---

attr_accessible specifies that you can not mass-assign attributes, using save method, for example. So, if you change an attribute that is not defined with attr_accessible, you will get a warning because it will not actually be saved in the database.