RT，学习@Terry老师在http://railscasts-china.com 的视频教程时，我电脑使用的 rails 版本: rails -v:Rails 3.2.6,每次生产一个 model 时。都会在 model 中自动加上 attr_accessible，现在用 omniauth 时，出现了这个问题，代码是这样的，

class User < ActiveRecord::Base
  attr_accessible :email, :nickname
  validates :nickname, :presence => true
  validates :email, :presence => true, :uniqueness => true
  has_many :authentications
  has_many :posts

  accepts_nested_attributes_for :authentications

  def add_auth(auth)
    authentications.create(:provider => auth[:provider],
      :uid => auth[:uid])
  end

  class << self
    def from_auth(auth)
      locate_auth(auth) || locate_email(auth) || create_auth(auth)
    end

    def locate_auth(auth)
      Authentication.find_by_provider_and_uid(auth[:provider],
                                              auth[:uid]).try(:user)
    end

    def locate_email(auth)
      user = find_by_email(auth[:info][:email])
      return unless user
      user.add_auth(auth)
      user
    end

    def create_auth(auth)
      create!(
        :nickname => auth[:info][:nickname],
        :email => auth[:info][:email],
        :authentications_attributes => [
          Authentication.new(:provider => auth[:provider],
                             :uid => auth[:uid]
                            ).attributes
      ])

    end
  end
end

代码是视频教程中@Terry老师的，我自己手动打出来的。第二行attr_accessible :email, :nickname是生成这个 model 时自己生成的. 现在我访问http://127.0.0.1:3000/auth/github/ 或者http://127.0.0.1:3000/auth/identity/register 时，都会报这个错误：

ActiveModel::MassAssignmentSecurity::Error in SessionsController#create

Can't mass-assign protected attributes: authentications_attributes

其中 SessionsController 中的代码是这样的：

class SessionsController < ApplicationController
  def create
    user = User.from_auth(request.env['omniauth.auth'])
    session[:user_id] = user.id
    flash[:notice] = "Welcome #{user.nickname}"
    redirect_to posts_path
  end

  def new
    flash[:failure_provider] = request.env['omniauth.error.strategy'].name
    flash[:failure_type] = request.env['omniauth.error.type']
  end
end

. 自己尝试这样解决: 将authentications_attributes也加在user_model 的 attr_accessible :email, :nickname中，即 attr_accessible :email, :nickname, :authentications_attributes,这时，又报错

ActiveModel::MassAssignmentSecurity::Error in SessionsController#create

Can't mass-assign protected attributes: created_at, updated_at

发到这里，恳请各位帮忙下。谢谢~