How can you make a variable available to the result of every Rails action?

Question

Let's say you have a config variable for facebook app id defined as:

TestSiteRails::Application.configure do
  config.facebook_app_id = '123146123188122'
end

You want this variable to be available in every action, so that it's available in the main layout, application.html.haml:

!!! html
%html
  %head
  %body
    #fb-root
    :javascript
      window.fbAsyncInit = function() {
        // init the FB JS SDK
        FB.init({
          appId      : '#{@facebook_app_id}', // Configured facebook app id
          channelUrl : '//WWW.YOUR_DOMAIN.COM/channel.html', // Channel File for x-domain communication
          status     : true, // check the login status upon init?
          cookie     : true, // set sessions cookies to allow your server to access the session?
          xfbml      : true  // parse XFBML tags on this page?
        });

    = yield :contents 

Rather than repeating the code to do this in each controller action, how can I make this available to every action?

Answer 1

You could put it into your ApplicationController, so that all controllers inherit it:

class ApplicationController
  before_filter :set_facebook_app_id

  private

  def set_facebook_app_id
    @facebook_app_id ||= Rails.configuration.facebook_app_id
  end
end

Or, if you need it to be accessible to views too, as a helper method:

class ApplicationController
  def facebook_app_id
    Rails.configuration.facebook_app_id
  end
  helper_method :facebook_app_id
end

Answer 2

您可以在application_controller中使用before_filter ，但我认为如果要使用它具有常量ID，则可以使用常量。