Site Config (config.yml) for Rails

Over at Railscasts, The Honourable Ryan Bates, Esquire¹ has been churning out quality screencasts FOREVER. And while some of them become somewhat obsolete as Rails itself changes, they're still a better starting point than most of what's available on the web.

One that I happened to view recently concerned application configuration for your Rails app being stored in a .yml file. This brings site configuration in line with database, fixtures, etc. As usual, Ryan gives you exactly what you need to adapt things to your situation. So I did. This is my ApplicationConfiguration class.² It basically gives you a global ::AppConfig object, which allows you to reverence any of your configuration settings from a single place. It supports nested configuration, and automatically selects the right environment (test, production, etc).

# config/initializers/_init_app_config.rb
class ApplicationConfigurationNode
  def initialize( data )
    data.each do |k,v|
      self.assign_value( k, v )
    end
  end

  def assign_value( name, val )
    if val.is_a?( Hash )
      self.instance_variable_set( "@#{name.to_s}".to_sym, ApplicationConfiguration.new( val ) )
    else
      self.instance_variable_set( "@#{name.to_s}".to_sym, val )
    end
  end

  def method_missing( name, *args )
    if name.to_s =~ /(.*)=$/
      self.assign_value( $1, args.first )
    else
      if self.instance_variable_defined?( "@#{name.to_s}".to_sym )
        self.instance_variable_get( "@#{name.to_s}".to_sym )
      else
        nil
      end
    end
  end
end

class ApplicationConfiguration < Rails::OrderedOptions
  def initialize
    config_file = "#{RAILS_ROOT}/config/config.yml"
    if File.exists?( config_file )
      config_hash = YAML.load_file( config_file )
      if config_hash.has_key?( RAILS_ENV )
        @parameters = ApplicationConfigurationNode.new( config_hash[RAILS_ENV] )
      end
    end
  end

  def method_missing( name, *args )
    @parameters.method_missing( name, args.first )
  end
end

::AppConfig = ApplicationConfiguration.new

I put this in config/initializers/_init_app_config.rb, so that it gets loaded before everything else, and I'm done. Now I'm free to add whatever I want to config.yml and reference it from anywhere in my app.

# config/config.yml
test:
  harsh:
    theme: 'twilight'
production:
  harsh:
    theme: 'spacecadet'

# app/views/layouts/_stylesheets.html.erb
# ...
<%= stylesheet_link_tag 'harsh/#{::AppConfig.harsh.theme}' %>
# ...

¹All titles bestowed only by me. Keep your attorneys to yourself.

²I know I saw someone doing something similar to this, but for the life of me I can't find it. If it was you, I apologize for not giving credit.