试图让omniauth-facebook工作未定义的方法`user_id'为nil：NilClass rails

我正在使用ryan bates facebook身份验证railscast和coderwall上的这篇文章来实现omniauth-facebook的登录功能

https://coderwall.com/p/bsfitw

所以对于我的gemfile，我有这两个

gem 'omniauth'
gem 'omniauth-facebook'

这是我的omniauth.rb

OmniAuth.config.logger = Rails.logger

Rails.application.config.middleware.use OmniAuth::Builder do
  provider :facebook, 'commentedoutappid', 'commentedoutsecretid'
end

我的路线看起来像这样

match 'auth/:provider/callback', to: 'sessions#create', via: [:get, :post]
  match 'auth/failure', to: redirect('/'), via: [:get, :post]
  match 'signout', to: 'sessions#destroy', as: 'signout', via: [:get, :post]

  resources :movies do 
    resources :reviews
  end 
  root to: 'movies#index'

这是我的会话控制器

class SessionsController < ApplicationController
  def create
    user = User.from_omniauth(env["omniauth.auth"])
    session[:user_id] = current_user.user_id 
    redirect_to root_url
  end
end

这是我的用户模型

class User < ActiveRecord::Base
  def self.from_omniauth(auth)
    where(auth.slice(:provider, :uid)).first_or_initialize.tap do |user|
      user.provider = auth.provider 
      user.uid = auth.uid
      user.name = auth.info.name
      user.oauth_token = auth.credentials.oauth_token 
      user.oauth_expires_at = Time.at(auth.credentials.expires_at)
      user.save
     end
   end 
end

这是我的用户表

create_table "users", force: true do |t|
    t.string   "provider"
    t.string   "uid"
    t.string   "name"
    t.string   "oauth_token"
    t.datetime "oauth_expires_at"
    t.datetime "created_at"
    t.datetime "updated_at"
    t.string   "email",                  default: "", null: false
    t.string   "encrypted_password",     default: "", null: false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          default: 0,  null: false
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
  end

我在application.html.erb中有这些链接

<div id="user-widget">
  <% if current_user %>
    Signed in as <strong><%= current_user.name %></strong>!
    <%= link_to "Sign out", signout_path, id: "sign_out" %>
  <% else %>
    <%= link_to "Sign in with facebook", "/auth/facebook", id: "sign_in" %>
  <% end %>
</div>

当我点击指向auth / facebook的链接时

我在会话控制器中获取了 undefined method user_id'为nil：NilClass` .

哦，我也有一个current_user帮助方法

class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception

  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end 
  helper_method :current_user
end

到目前为止，我完全理解流程，但不理解错误 . 我完全按照指南从上到下 .

我开始使用空白的rails 4应用程序 . 我甚至尝试过安装设备，因此有一个current_user，但我最终卸载了设计因为它们发生了冲突 .