How to define custom configuration variables in Rails?

In Rails 3, Application specific custom configuration data can be placed in the application configuration object. The configuration can be assigned in the initialization files or the environment files -- say for a given application MyApp:

MyApp::Application.config.custom_config_variable = :my_config_setting

or

Rails.configuration.custom_config_variable = :my_config_setting

To read the setting, simply call the configuration variable without setting it:

Rails.configuration.custom_config_variable
=> :my_config_setting

UPDATE Rails 4

In Rails 4 there a new way for this => http://guides.rubyonrails.org/configuring.html#custom-configuration

https://i.stack.imgur.com/ASdRg.png

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Update 1

Very recommended: I'm going with Rails Config gem nowadays for the fine grained control it provides.

Update2

If you want a quick solution, then check Jack Pratt's answer below.

Although my original answer below still works, this answer is now outdated. I recommend looking at updates 1 and 2.

Original Answer:

For a quick solution, watching the "YAML Configuration File" screen cast by Ryan Bates should be very helpful.

In summary:

# config/initializers/load_config.rb
APP_CONFIG = YAML.load_file("#{Rails.root}/config/config.yml")[Rails.env]

# application.rb
if APP_CONFIG['perform_authentication']
  # Do stuff
end

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In Rails 3.0.5, the following approach worked for me:

In config/environments/development.rb, write

config.custom_config_key = :config_value

The value custom_config_key can then be referenced from other files using

Rails.application.config.custom_config_key

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In Rails 4

Assuming you put your custom variables into a yaml file:

# config/acme.yml
development:
  :api_user: 'joe'
  :api_pass: 's4cret'
  :timeout: 20

Create an initializer to load them:

# config/initializers/acme.rb
acme_config = Rails.application.config_for :acme

Rails.application.configure do
  config.acme = ActiveSupport::OrderedOptions.new
  config.acme.api_user = acme_config[:api_user]
  config.acme.api_pass = acme_config[:api_pass]
  config.acme.timeout  = acme_config[:timeout]
end

Now anywhere in your app you can access these values like so:

Rails.configuration.acme.api_user

It is convenient that Rails.application.config_for :acme will load your acme.yml and use the correct environment.

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This works in rails 3.1:

in config/environment.rb (or in config/environments/.. to target a specific environment) :

YourApp::Application.config.yourKey = 'foo'

This will be accessible in controller or views like this:

YourApp::Application.config.yourKey

(YourApp should be replaced by your application name.)

Note: It's Ruby code, so if you have a lot of config keys, you can do this :

in config/environment.rb :

YourApp::Application.configure do
  config.something = foo
  config.....
  config....
  .
  config....
end

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Since Rails 4.2, without additional gems, you can load config/hi.yml simply by using Rails.application.config_for :hi.

For example:

touch config/passwords.yml #config/passwords.yml development: username: 'a' password: 'b' production: username: 'aa' password: 'bb'

touch config/initializers/constants.rb #config/initializers/constants.rb AUTHENTICATION = Rails.application.config_for :passwords

and now you can use AUTHENTICATION constant everywhere in your application: #rails c production :001> AUTHENTICATION['username'] => 'aa' then add passwords.yml to .gitignore: echo /config/passwords.yml >> .gitignore, create an example file for your comfort cp /config/passwords.yml /config/passwords.example.yml and then just edit your example file in your production console with actual production values.

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I just wanted to update this for the latest cool stuff in Rails 4.2, you can now do this inside any of your config/**/*.rb files:

config.x.whatever.you.want = 42

...and this will be available in your app as:

Rails.configuration.x.whatever.you.want

See more here: http://guides.rubyonrails.org/configuring.html#custom-configuration

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Rails 6

Many outdated answers, so adding one that is specific to Rails 6.

Application specific configuration goes in initializer files. Details are here: edge guides

Example:

config/initializers/foo.rb

module MyApp
  class Application < Rails::Application
    config.test_val = 'foo'
  end
end

Alternatively:

Rails.application.config.test_val = 'foo'

This can now be accessed as:

Rails.configuration.test_val

Many more possibilities. edge guides #custom-configuration

ex, you can also set up nested namespace configurations:

config.x.payment_processing.schedule = :daily
config.x.payment_processing.retries  = 3
config.super_debugger = true

or use config_for to load entire custom config files:

config/payment.yml

production:
  environment: production
  merchant_id: production_merchant_id
  public_key:  production_public_key
  private_key: production_private_key

development:
  environment: sandbox
  merchant_id: development_merchant_id
  public_key:  development_public_key
  private_key: development_private_key

Then load it with:

config/initializers/load_payment.rb

module MyApp
  class Application < Rails::Application
    config.payment = config_for(:payment)
  end
end

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Check out this neat gem doing exactly that: https://github.com/mislav/choices

This way your sensitive data won't be exposed in open source projects

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I created a simple plugin for YAML settings: Yettings

It works in a similar fashion to the code in khelll's answer, but you only need to add this YAML configuration file:

app/config/yetting.yml

The plugin dynamically creates a class that allows you to access the YML settings as class methods in your app like so:

Yetting.your_setting

Also, if you want to use multiple settings files with unique names, you can place them in a subdirectory inside app/config like this:

app/config/yettings/first.yml
app/config/yettings/second.yml

Then you can access the values like this:

FirstYetting.your_setting
SecondYetting.your_setting

It also provides you with default settings that can be overridden per environment. You can also use erb inside the yml file.

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I really like the settingslogic gem. Very easy to set up and use.

https://github.com/binarylogic/settingslogic

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If you use Heroku or otherwise have need to keep your application settings as environment variables, the figaro gem is very helpful.

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I like to use rails-settings for global configuration values that need to be changeable via web interface.

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Something we've starting doing at work is the ActiveSupport Ordered Hash

Which allows you to define your configuration cleanly inside the environment files e.g.

config.service = ActiveSupport::OrderedOptions.new
config.service.api_key = ENV['SERVICE_API_KEY']
config.service.shared_secret = ENV['SERVICE_SHARED_SECRET']

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I would suggest good approach how to deal with configuration in your application at all. There are three basic rules:

change your configuration not a code;

use configurations over conditions;

write code that means something.

To have more detailed overview follow this link: Rails configuration in the proper way

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