Railscasts #241 NoMethodError undefined method `[]' for nil:NilClass

Question

SessionsController#create 中存在 NoMethodError。出现 twitter 身份验证页面，但回调 URL 不起作用。推特身份验证后，该页面未呈现到网站。 这是不同文件中的代码。

在 routes.rb 中

Blog::Application.routes.draw do
  root :to => "posts#index"

  match "/auth/:provider/callback" => "sessions#create"
  match "/signout" => "sessions#destroy", :as => :signout

  resources :posts
end

在 session_controller.rb 中

class SessionsController < ApplicationController
  def create
    auth = request.env["omniauth.auth"]
    user = User.find_by_provider_and_uid(auth["provider"], auth["uid"]) || User.create_with_omniauth(auth)
    session[:user_id] = user.id
    redirect_to root_url, :notice => "Signed in!"
  end

  def destroy
    session[:user_id] = nil
    redirect_to root_url, :notice => "Signed out!"
  end
end

在user.rb中

class User < ActiveRecord::Base
  def self.create_with_omniauth(auth)
    create! do |user|
      user.provider = auth["provider"]
      user.uid = auth["uid"]
      user.name = auth["user_info"]["name"]
    end
  end
end

完整跟踪：

app/models/user.rb:6:in `block in create_with_omniauth'
activerecord (3.2.0) lib/active_record/validations.rb:40:in `create!'
app/models/user.rb:3:in `create_with_omniauth'
app/controllers/sessions_controller.rb:4:in `create'
actionpack (3.2.0) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (3.2.0) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.0) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.0) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.0) lib/active_support/callbacks.rb:414:in `_run__168269495__process_action__8122527__callbacks'
activesupport (3.2.0) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.0) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.0) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.0) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.0) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.0) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.0) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.0) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.0) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.0) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.0) lib/action_controller/metal/params_wrapper.rb:205:in `process_action'
activerecord (3.2.0) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.0) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.0) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.0) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.0) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.0) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.0) lib/action_dispatch/routing/route_set.rb:66:in `call'
actionpack (3.2.0) lib/action_dispatch/routing/route_set.rb:66:in `dispatch'
actionpack (3.2.0) lib/action_dispatch/routing/route_set.rb:30:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `block in call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.0) lib/action_dispatch/routing/route_set.rb:570:in `call'
omniauth (1.1.4) lib/omniauth/strategy.rb:401:in `call_app!'
omniauth (1.1.4) lib/omniauth/strategy.rb:363:in `callback_phase'
omniauth-oauth (1.0.1) lib/omniauth/strategies/oauth.rb:58:in `callback_phase'
omniauth (1.1.4) lib/omniauth/strategy.rb:226:in `callback_call'
omniauth (1.1.4) lib/omniauth/strategy.rb:182:in `call!'
omniauth (1.1.4) lib/omniauth/strategy.rb:164:in `call'
omniauth (1.1.4) lib/omniauth/builder.rb:49:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.5) lib/rack/etag.rb:23:in `call'
rack (1.4.5) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.5) lib/rack/session/abstract/id.rb:210:in `context'
rack (1.4.5) lib/rack/session/abstract/id.rb:205:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/cookies.rb:338:in `call'
activerecord (3.2.0) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:443:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.0) lib/active_support/callbacks.rb:405:in `_run__208198798__call__80088063__callbacks'
activesupport (3.2.0) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.0) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.0) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.0) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.0) lib/rails/rack/logger.rb:26:in `call_app'
railties (3.2.0) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.5) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.5) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.0) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.5) lib/rack/lock.rb:15:in `call'
actionpack (3.2.0) lib/action_dispatch/middleware/static.rb:53:in `call'
railties (3.2.0) lib/rails/engine.rb:479:in `call'
railties (3.2.0) lib/rails/application.rb:220:in `call'
rack (1.4.5) lib/rack/content_length.rb:14:in `call' 
railties (3.2.0) lib/rails/rack/log_tailer.rb:14:in `call'
rack (1.4.5) lib/rack/handler/webrick.rb:59:in `service'
/home/sakshi/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
/home/sakshi/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
/home/sakshi/.rvm/rubies/ruby-2.0.0-p195/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'

控制台：

NoMethodError (undefined method `[]' for nil:NilClass):
  app/models/user.rb:6:in `block in create_with_omniauth'
  app/models/user.rb:3:in `create_with_omniauth'
  app/controllers/sessions_controller.rb:4:in `create'

Answer 1

app/models/user.rb 的第 6 行：

user.name = auth["user_info"]["name"]

auth 哈希没有“user_info”键的值，因此它返回nil；然后你尝试在 nil 上调用 [] 方法，这会引发异常。

尝试在块中添加p auth 以验证auth 哈希内容：

class User < ActiveRecord::Base
  def self.create_with_omniauth(auth)
    create! do |user|
      puts "DEBUG " + "=" * 50
      p auth
      user.provider = auth["provider"]
      user.uid = auth["uid"]
      user.name = auth["user_info"]["name"]
    end
  end
end

Answer 2

在这一行进行了更改：

user.name = auth["info"]["name"]

它有效。