ActionDispatch::Flash < Objec

pass temporary primitive-types (String, Array, Hash) between actions.

Anything you place in the flash will be exposed to the very next action and then cleared out.

用于增加通知，警告信息，例子：

def create

 flash[:notice] = "Post successfully created"

 redirect_to @post

end 

模块ActionController::Flash里面有一个实例私有方法：

redirect_to(options = {}, response_status_and_flash = {})可以把flash信息做参数返回到下一个action.

例子：redirect_to(store_index_path, notice: "...")

ActionDispatch::Flash::FlashHash < Object 有20多个方法：

如alert, notice, 可以用chain方式写法：flash.notice = "..."

keep(k = nil):

Keeps either the entire current flash or a specific flash entry available for the next action:

flash.keep # keeps the entire flash 

flash.keep(:notice) # keeps only the "notice" entry, 

the rest of the flash is discarded

now() ：只能用于在当前动作下使用

Sets a flash that will not be available to the next action, only to the current.

flash.now[:message] = "Hello current action"

ModuleActiveSupport::Rescuable::ClassMethods

用在对类的错误的营救：

rescue_from(*klasses, with: nil, &block)

Rescue exceptions raised in controller actions.

参数1:a series of exception classes or class names,

参数2: and a trailing :with option with the name of a method or a Proc object to be called to handle them. Alternatively a block can be given.

class ApplicationController < ActionController::Base

rescue_from User::NotAuthorized, with: :deny_access # self defined exception

rescue_from ActiveRecord::RecordInvalid, with: :show_errors

rescue_from 'MyAppError::Base' do |exception|

render xml: exception, status: 500

end

private

def deny_access

...

end

def show_errors(exception)

exception.record.new_record? ? ...

end

end

Rails 使用 ActiveSupport::Logger 类把信息写入日志。

在log文件内隐藏着development.log, test.log.

guide指导：http://guides.rubyonrails.org/debugging_rails_applications.html#the-logger

每一个控制器都有logger属性，可以在其中的action中增加logger.XXX()方法。

 logger.debug "New article: #{@article.attributes.inspect}"

Sending Messages

To write in the current log use the logger.(debug|info|warn|error|fatal) from within a controller, model or mailer。控制器，模块，邮件模块，都可以添加logger.xxx()方法。