ReadWriteSettings is a simple configuration / settings solution that uses an ERB enabled YAML file. It has been great for our apps, maybe you will enjoy it too. ReadWriteSettings works with Rails, Sinatra, or any Ruby project.

It is a fork of ReadWriteSettings[] to support modifications and additional getting/setter methods. Hopefully can merge this fork back into ReadWriteSettings in future and have a single project again.


Add the following to your Gemfile:

gem "readwritesettings"


1. Define your class

Instead of defining a Settings constant for you, that task is left to you. Simply create a class in your application that looks like:

class Settings < ReadWriteSettings
  source "#{Rails.root}/config/application.yml"
  namespace Rails.env

Name it Settings, name it Config, name it whatever you want. Add as many or as few as you like. A good place to put this file in a rails app is app/models/settings.rb

I felt adding a settings file in your app was more straightforward, less tricky, and more flexible.

Alternately, you can pass a Hash into the constructor.

Settings ={"key" => "value"})

2. Create your settings

Notice above we specified an absolute path to our settings file called "application.yml". This is just a typical YAML file. Also notice above that we specified a namespace for our environment. A namespace is just an optional string that corresponds to a key in the YAML file.

Using a namespace allows us to change our configuration depending on our environment:

# config/application.yml
defaults: &defaults
    saweet: nested settings
  neat_setting: 24
  awesome_setting: <%= "Did you know 5 + 5 = #{5 + 5}?" %>

  <<: *defaults
  neat_setting: 800

  <<: *defaults

  <<: *defaults

Note: Certain Ruby/Bundler versions include a version of the Psych YAML parser which incorrectly handles merges (the << in the example above.) If your default settings seem to be overwriting your environment-specific settings, including the following lines in your config/boot.rb file may solve the problem:

require 'yaml'
YAML::ENGINE.yamler= 'syck'

3. Access your settings

>> Rails.env
=> "development"

=> "#<ReadWriteSettings::Settings ... >"

=> "nested settings"

>> Settings.neat_setting
=> 800

>> Settings.awesome_setting
=> "Did you know 5 + 5 = 10?"

You can use these settings anywhere, for example in a model:

class Post < ActiveRecord::Base
  self.per_page = Settings.pagination.posts_per_page

4. Optional / dynamic settings

Often, you will want to handle defaults in your application logic itself, to reduce the number of settings you need to put in your YAML file. You can access an optional setting by using Hash notation:

>> Settings.messaging.queue_name
=> Exception: Missing setting 'queue_name' in 'message' section in 'application.yml'

>> Settings.messaging['queue_name']
=> nil

>> Settings.messaging['queue_name'] ||= 'user_mail'
=> "user_mail"

>> Settings.messaging.queue_name
=> "user_mail"

Modifying our model example:

class Post < ActiveRecord::Base
  self.per_page = Settings.posts['per_page'] || Settings.pagination.per_page

This would allow you to specify a custom value for per_page just for posts, or to fall back to your default value if not specified.

5. Suppressing Exceptions Conditionally

Raising exceptions for missing settings helps highlight configuration problems. However, in a Rails app it may make sense to suppress this in production and return nil for missing settings. While it's useful to stop and highlight an error in development or test environments, this is often not the right answer for production.

class Settings < ReadWriteSettings
  source "#{Rails.root}/config/application.yml"
  namespace Rails.env
  suppress_errors Rails.env.production?

>> Settings.non_existent_key
=> nil

Note on Sinatra / Capistrano / Vlad

Each of these frameworks uses a +set+ convention for settings, which actually defines methods in the global Object namespace:

set :application, "myapp"  # does "def application" globally

This can cause collisions with ReadWriteSettings, since those methods are global. Luckily, the solution is to just add a call to load! in your class:

class Settings < ReadWriteSettings
  source "#{Rails.root}/config/application.yml"
  namespace Rails.env

It's probably always safest to add load! to your class, since this guarantees settings will be loaded at that time, rather than lazily later via method_missing.

Finally, you can reload all your settings later as well:


This is useful if you want to support changing your settings YAML without restarting your app.


This project was originally created by Ben Johnson and called ReadWriteSettings. A renamed fork was created so that new gem versions could be released with new functionality, by Dr Nic Williams. The latter is not entirely thrilled about this situation; but at least he now has a versioned gem with the new shiny stuff in it.

Copyright (c) 2008-2010 Johnson[] of Logic[], released under the MIT license. Support for optional settings and reloading by Wiger[].

Copyright (c) 2013 Nic Williams[]