在Ruby on Rails中，未定义方法`log_in`。
在Ruby on Rails中，未定义方法`log_in`。
我正在阅读Michael Hartl的Ruby on Rails教程的第8章。在8.2.1节的log_in方法中，当调用log_in user时，在SessionsController#create中出现了NoMethodError。它与这个链接问题几乎完全相同，但我仍然被卡住了，不知道原因在哪里。
我的当前代码：
class SessionsController < ApplicationController
def create
user = User.find_by(email: params[:session][:email].downcase)
if user && user.authenticate(params[:session][:password])
log_in user
redirect_to user
else
flash.now[:danger] = 'Invalid email/password combination'
render 'new'
end
end
end
class ApplicationController < ActionController::Base
protect_from_forgery with: :exception
include SessionsHelper
end
module SessionsHelper
def log_in(user)
session[:user_id] = user.id
end
end
如果我将log_in移动到SessionsController中，它可以正常工作，但我无法弄清楚为什么控制器不能在SessionsHelper中使用该方法。我已经重新启动了rails服务器，并确保一切已保存。我肯定是忽略了什么，但我自己看不到。
有什么想法吗？
编辑：
完整的Trace Stack:
Started POST "/login" for ....
ActiveRecord::SchemaMigration Load (0.2ms) SELECT "schema_migrations".* FROM "schema_migrations"
Processing by SessionsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"D/F/6LjqRPOF3FGVqUxq8VheYVqtqPb3ozAtRUkj2O5jBrb4IVfCPFl3FH2nsMGs4h6hzyC5EuUgevUqGfYheA==", "session"=>{"email"=>"gmichael@example.com", "password"=>"[FILTERED]"}, "commit"=>"Log in"}
User Load (0.3ms) SELECT "users".* FROM "users" WHERE "users"."email" = ? LIMIT ? [["email", "gmichael@example.com"], ["LIMIT", 1]]
#
Did you mean? login_url>
/home/ubuntu/workspace/sample_app/app/controllers/sessions_controller.rb:10:in `create'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_controller/metal/basic_implicit_render.rb:4:in `send_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/abstract_controller/base.rb:188:in `process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_controller/metal/rendering.rb:30:in `process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/abstract_controller/callbacks.rb:20:in `block in process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:126:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:506:in `block (2 levels) in compile'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:455:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:101:in `__run_callbacks__'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:750:in `_run_process_action_callbacks'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:90:in `run_callbacks'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/abstract_controller/callbacks.rb:19:in `process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_controller/metal/rescue.rb:20:in `process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_controller/metal/instrumentation.rb:32:in `block in process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/notifications.rb:164:in `block in instrument'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/notifications/instrumenter.rb:21:in `instrument'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/notifications.rb:164:in `instrument'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_controller/metal/instrumentation.rb:30:in `process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_controller/metal/params_wrapper.rb:248:in `process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-5.0.1/lib/active_record/railties/controller_runtime.rb:18:in `process_action'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/abstract_controller/base.rb:126:in `process'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionview-5.0.1/lib/action_view/rendering.rb:30:in `process'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_controller/metal.rb:190:in `dispatch'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_controller/metal.rb:262:in `dispatch'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/routing/route_set.rb:50:in `dispatch'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/routing/route_set.rb:32:in `serve'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/journey/router.rb:39:in `block in serve'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/journey/router.rb:26:in `each'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/journey/router.rb:26:in `serve'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/routing/route_set.rb:725:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/rack-2.0.1/lib/rack/etag.rb:25:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/rack-2.0.1/lib/rack/conditional_get.rb:38:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/rack-2.0.1/lib/rack/head.rb:12:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/rack-2.0.1/lib/rack/session/abstract/id.rb:222:in `context'
/usr/local/rvm/gems/ruby-2.3.0/gems/rack-2.0.1/lib/rack/session/abstract/id.rb:216:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/cookies.rb:613:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/activerecord-5.0.1/lib/active_record/migration.rb:553:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/callbacks.rb:38:in `block in call'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:97:in `__run_callbacks__'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:750:in `_run_call_callbacks'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/callbacks.rb:90:in `run_callbacks'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/callbacks.rb:36:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/executor.rb:12:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/remote_ip.rb:79:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/debug_exceptions.rb:49:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/web-console-3.1.1/lib/web_console/middleware.rb:131:in `call_app'
/usr/local/rvm/gems/ruby-2.3.0/gems/web-console-3.1.1/lib/web_console/middleware.rb:20:in `block in call'
/usr/local/rvm/gems/ruby-2.3.0/gems/web-console-3.1.1/lib/web_console/middleware.rb:18:in `catch'
/usr/local/rvm/gems/ruby-2.3.0/gems/web-console-3.1.1/lib/web_console/middleware.rb:18:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/show_exceptions.rb:31:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/railties-5.0.1/lib/rails/rack/logger.rb:36:in `call_app'
/usr/local/rvm/gems/ruby-2.3.0/gems/railties-5.0.1/lib/rails/rack/logger.rb:24:in `block in call'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/tagged_logging.rb:69:in `block in tagged'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/tagged_logging.rb:26:in `tagged'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/tagged_logging.rb:69:in `tagged'
/usr/local/rvm/gems/ruby-2.3.0/gems/railties-5.0.1/lib/rails/rack/logger.rb:24:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/sprockets-rails-3.2.0/lib/sprockets/rails/quiet_assets.rb:13:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/request_id.rb:24:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/rack-2.0.1/lib/rack/method_override.rb:22:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/rack-2.0.1/lib/rack/runtime.rb:22:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/activesupport-5.0.1/lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/executor.rb:12:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/actionpack-5.0.1/lib/action_dispatch/middleware/static.rb:136:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/rack-2.0.1/lib/rack/sendfile.rb:111:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/railties-5.0.1/lib/rails/engine.rb:522:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/puma-3.4.0/lib/puma/configuration.rb:224:in `call'
/usr/local/rvm/gems/ruby-2.3.0/gems/puma-3.4.0/lib/puma/server.rb:569:in `handle_request'
/usr/local/rvm/gems/ruby-2.3.0/gems/puma-3.4.0/lib/puma/server.rb:406:in `process_client'
/usr/local/rvm/gems/ruby-2.3.0/gems/puma-3.4.0/lib/puma/server.rb:271:in `block in run'
/usr/local/rvm/gems/ruby-2.3.0/gems/puma-3.4.0/lib/puma/thread_pool.rb:114:in `block in spawn_thread'
No template found for SessionsController#create, rendering head :no_content
Completed 204 No Content in 155ms (ActiveRecord: 1.0ms)
在我的情况下，这个问题通过删除[:session]并且我的登录URL与log_in不同，而是使用login_url来解决。以下是解决方法：
def create
user = User.find_by(email: params[:email])
if user && user.authenticate(params[:password])
login_url user
redirect_to user
else
flash[:danger] = 'Invalid email/password combination' # Not quite right!
render 'new'
end
end
希望能够解决问题。
在Ruby on Rails中，出现了Undefined method `log_in'的问题。这个问题的原因是在控制器中调用了helpers方法，然后使用log_in方法，但是该方法并不存在。
解决这个问题的方法是通过在控制器中引入相应的模块或类来使用log_in方法。根据给出的信息，可以通过调用helpers方法来访问控制器中的帮助器。在这种情况下，可以尝试使用helpers.log_in user来调用log_in方法。
然而，需要注意的是，这种做法可能是一个反模式。在Ruby on Rails中，控制器负责处理请求和响应，而帮助器主要用于视图层和模板中的逻辑处理。直接在控制器中调用帮助器方法可能会破坏MVC架构的原则，导致代码的可读性和可维护性降低。
因此，在解决这个问题时，建议重新考虑代码的组织结构和逻辑。如果需要在控制器中使用某个方法，可以将该方法定义在控制器本身或者通过模块的方式引入。这样可以更好地遵循Rails的设计原则和最佳实践。
以上是关于Undefined method `log_in'问题的原因和解决方法的整理。如果需要了解更多关于Rails帮助器的信息，可以参考https://www.rubyguides.com/2020/01/rails-helpers/。
在Ruby on Rails中出现Undefined method `log_in'的错误，可能的原因是没有定义log_in方法或者没有将其定义为helper方法。解决方法是在SessionsHelper中添加helper_method :log_in，并确保SessionsHelper文件位于Rails默认查找的位置。如果SessionsHelper文件位于lib目录或其他Rails默认不查找的位置，则需要自动加载它们。
首先，可以尝试在SessionsHelper中添加helper_method :log_in。这可以通过在SessionsHelper文件中添加helper_method :log_in来实现。这将把log_in方法定义为helper方法，使其在视图中可用。
如果添加helper_method :log_in后仍然出现错误，可以尝试将helper_method调用放在ApplicationController中。这可以通过将helper_method :log_in移动到ApplicationController文件中来实现。这是因为helper_method方法只在ApplicationController中定义。
另外，需要确保SessionsHelper文件位于Rails默认查找的位置。根据问题描述，sessions_helper.rb位于app\controllers\helpers目录中。这是Rails默认查找helper文件的位置，所以应该是正确的。
如果SessionsHelper文件位于lib目录或其他Rails默认不查找的位置，需要确保自动加载它们。可以参考链接http://stackoverflow.com/questions/19098663了解如何自动加载lib目录中的文件。
如果上述方法都无法解决问题，建议提供完整的错误信息和堆栈跟踪，以便更好地理解问题所在。这可以通过将错误信息和堆栈跟踪添加到问题描述中来实现。