Simple Config is a plugin designed to make application-wide configuration settings easy to set and access in an object-oriented fashion.
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Simple Config is a plugin designed to make application-wide configuration settings easy to set and access in an
object-oriented fashion.

Rails already provides a way of configuring the framework on a per-environment basis but other than global variables/constants set in each environment file or environment.rb, there isn’t a built-in way of providing application-specific settings.

One simple solution is to simply put all of your app configuration into a YAML file and load this somewhere in your environment, but I wanted something a little bit more flexible that we could use across all of our applications and Simple Config is what we came up with.

SimpleConfig was originally written against Rails 1.x and may still work but as of version 1.1.1 the minimum required Rails version is 2.3.5. You may be able to use it with older versions of Rails but YMMV.

Getting started

The plugin comes with a rake task to get you up and running quickly, so start by running that.

$ rake simple_config:setup

This will create a config/settings folder and a blank settings file for each of the main Rails environments. It will also create a copy of the SimpleConfig initializer in config/initializers/configuration.rb.

Now, if you open up the configuration.rb initializer, you will see something like this:

SimpleConfig.for :application do

  # your app configuration here
  load File.join(Rails.root, 'config', "settings", "#{RAILS_ENV}.rb"), :if_exists? => true
  load File.join(Rails.root, 'config', "settings", "local.rb"),        :if_exists? => true

This is where you can set any configuration variables that are required across all Rails environments. The load method works just like Ruby’s built-in load method, except the contents of the file it loads are evaluated within the context of the SimpleConfig.for block. The :if_exists? flag, when set to true, means that the file will only be loaded if it exists, otherwise it will simply be ignored.

Variables can be overwritten, and are defined in the order that they are loaded, so you can set up default values in the above file and override them in the environment files.

As well as loading a settings file for your current Rails environment, a file called “local.rb” is loaded which is designed as a place for you to override variables specific to your own development environment — you can just keep a copy of this locally without having to check it into your version control system1.


Setting Variables

Setting variables is simple and will be familiar to anybody who has used Capistrano. Whether in your main SimpleConfig.for block in configuration.rb, or one of your external settings files, use the set method:

SimpleConfig.for :application do
  set :my_variable, 'hello world'

SimpleConfig also supports a form of namespacing that allows you to group logical sets of variables together:

SimpleConfig.for :application do
  group :awesome_stuff do
    set :my_variable, 'hello world'

Both the set and load methods are available within group blocks and files loaded inside groups will be evaluated in the context of that group.

Whilst I’d recommend not nesting your groups more than one-level, there is no limit on how deep they can be nested.

Unsetting variables

Sometimes you might want to completely delete a variable from the collection. Simply setting its value to nil doesn’t work because nil might be a valid value.
You can delete a variable using the unset method.

SimpleConfig.for :application do
  set :my_variable, 'hello world'
  unset :my_variable

For instance, this is useful to remove global settings at environment level instead of overwriting the default value with a nonsense-one.
unset returns the value of the variable just in case you need to use it elsewhere.

Does a specific variable exist?

I don’t know but you can check it yourself using exists? method.

config = SimpleConfig.for :application do
  set :my_variable, 'hello world'

# write some nice code 
config.exists? :my_variable     # => true
config.exists? :your_variable   # => false

Accessing your configuration

SimpleConfig allows you set as many separate configurations as you like using the SimpleConfig.for method, which takes a symbol representing the configuration name, although most people will just create a single “application” config as above. To access this config from anywhere in your application, you can also use SimpleConfig.for method without a block, which always returns the named configuration object.

It is worth pointing out that SimpleConfig.for provides an almost singleton-style access to a particular named config. Calling SimpleConfig.for with a block a second time for a particular named configuration will simply extend the existing configuration, not overwrite it.

Once you have a reference to your configuration object, you can access variables using method access. Given the above example, :my_variable would be accessed in the following way:

config = SimpleConfig.for(:application)
config.my_variable # => "hello world"

Accessing grouped variables works as you would expect:

config = SimpleConfig.for(:application)
config.awesome_stuff.my_variable # => "hello world"

Using your configuration in your Rails app

The plugin provides a convenient mixin for your ApplicationController to make configuration access as simple as possible. Assuming a configuration called “application” (as in the above examples), it defines a config method which can be used in any of your controllers. It also defines this as a method as a view helper using the Rails helper_method macro so you can access configuration data in your views.

Note – there is no direct way of accessing your configuration variables in your models other than making a direct call to SimpleConfig.for. I’d recommend designing your models in such a way that configuration data can be passed into them at runtime as method arguments by your controller to avoid coupling your model to SimpleConfig.

To use the mixin, simply include it in your ApplicationController:

class ApplicationController < ActionController::Base
  include SimpleConfig::ControllerMixin

Then in your controllers:

class MyController < ApplicationController
  def index
    render :text => config.my_config_variable

The mixin provides also a class-level config method to access the configuration when you don’t have a controller instance available.

class MyController < ApplicationController
  protect_from_forgery :secret => config.secret_token

  def index
    render :text => config.my_config_variable

1 In fact, I recommend you make sure your version control system ignores this file otherwise you risk checking in a file that will override values in production! If you are using Subversion, simply add local.rb to the svn:ignore property for the config/settings folder.