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Action Pack and Controller Filters


In this fifteenth part of an eighteen-part series on the Action Pack library for Rails, you'll start learning how and why to use control filters. This article is excerpted from chapter six of the book Beginning Rails: From Novice to Professional, written by Jeffery Allan Hardy, Cloves Carneiro Jr. and Hampton Catlin (Apress; ISBN: 1590596862).

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By: Apress Publishing
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July 14, 2011
TABLE OF CONTENTS:
  1. · Action Pack and Controller Filters
  2. · Requiring Authentication with Filters

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Action Pack and Controller Filters - Requiring Authentication with Filters
(Page 2 of 2 )

In our events application, weve decided that we want to protect event creation and modification, restricting access only to registered users. To do this, well use filters that call specific methods and check for the user_id session we set upon user login. Recall that any methods we add to the application_controller are available to all other controllers (since its the superclass of all controllers).

Open the application_controller in app/controllers/application.rb and add the private methods that well use to enforce our authentication requirement, as shown in Listing 6-21.

Listing 6-21. Modified app/controllers/application.rb

class ApplicationController < ActionController::Base

protected

# Returns the currently logged in user or nil if there isn't one

def current_user

return unless session[:user_id ] @current_user ||= User.find_by_id(session[:user_id]) end

# Make current_user available in templates as a helper

helper_method :current_user

# Filter method to enforce a login requirement

# Apply as a before_filter on any controller you want to protect

def authenticate

logged_in? ? true : access_denied end

# Predicate method to test for a logged in user def logged_in? current_user.is_a? User end

# Make logged_in? available in templates as a helper

helper_method :logged_in?

def access_denied

flash[:notice] = "Please log in to continue"

redirect_to login_url and return false

end end

The current_user method acts like an accessor for the currently logged-in user. Since it returns a User object, we can call instance methods of User on it, such as current_user.login . The authenticate method is our filter method (the one well call from individual controllers). It checks whether there is a currently logged-in user via logged_in? (which, in turn, checks that there is actually a User returned by current_user ) and calls access_denied , if there isnt. access_denied sets a message in the flash and redi rects to the login action on the users controller.

We want two of these methods available in templates as well: logged_in? and current_user . Having logged_in? available will allow us to make dynamic decisions about whether or not a user is logged in. We can use this to show or hide administrative controls (such as adding or editing a given event). Having current_user around will also prove useful in templates, allowing us to access information about the users such as their login name or email address. Rails provides a handy way to extend the visibility of methods to templates by declaring them as helpers. You can use helper_method followed by a symbolic reference to the method in question, as weve done here. You can also pass an array of method references to helper_method if you want to declare them all at once.

Lets apply the filter to our events controller now. Well also apply a filter to the users controller to restrict who can edit user profiles.

Please check back regularly for the next part of the series.


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