Ruby On Rails 面试题与答案

Question: What is Filter and when is it called in Ruby on Rails?

Filters are methods that are called either before/after a controller action is called. 

Say a user requests a controller action such as userdashboard/index

In such a case a filter can be setup so that the UserDashboard/index page is only accessible to loggedin users by adding the following lines towards the beginning of the page:

class UserDashboardController < ApplicationController

  before_filter :confirm_logged_in,  :except => [:login, :attempt_login, :logout]
  
  def index
      ....
  end

  def login
      ....
  end

  def attempt_login
      ....
  end

  def logout
      ....
  end

end  

In the code above the condition �confirm_logged_in� is checked before all actions, except login, logout & attempt_login. 

After filters (after_filter) are not used too much but they have the effect of executing some code after a particular action has completed. 

Think of them like triggers that get executed automatically � just like a database trigger.