Configurate - A flexible configuration system

Configurate allows you to specify a chain of configuration providers which are queried in order until one returns a value. This allows scenarios like overriding your default settings with a user configuration file and let those be overridden by environment variables. The query interface allows to group and nest your configuration options to a practically unlimited level.

Configurate works with Ruby 1.9.2 or later.

Installation

Just add

gem 'configurate'

to your Gemfile.

Usage

A basic loader could look like this:

require 'configurate'

Config = Configurate::Settings.create do
  add_provider Configurate::Provider::Env
  add_provider Configurate::Provider::YAML, '/etc/app_settings.yml',
               namespace: Rails.env, required: false
  add_provider Configurate::Provider::YAML, 'config/default_settings.yml'
end

# Somewhere later
if Config.remote_assets.enable?
  set_asset_host Config.remote_assets.host
end

You can add custom methods working with your settings to your Configurate::Settings instance by calling extend YourConfigurationMethods inside the block passed to #create.

Providers are called in the order they're added. You can already use the added providers to determine if further ones should be added:

require 'configurate'

Config = Configurate::Settings.create do
  add_provider Configurate::Provider::Env
  add_provider Configurate::Provider::YAML, 'config/settings.yml' unless heroku?
end

add_provider can be called later on the created object to add more providers to the chain. It takes a constant and parameters that should be passed to the initializer.

A providers only requirement is that it responds to the #lookup method. #lookup is passed the current SettingPath, for example for a call to Config.foo.bar.baz? it gets a path with the items 'foo', 'bar', 'baz' passed. SettingPath behaves like Array with some methods added. The provider should raise Configurate::SettingNotFoundError if it can't provide a value for the requested option. Any additional parameters are passed along to the provider, thus a #lookup method must be able to take any number of additional parameters.

You're not limited to one instance of the configuration object.

Gotchas

False

Ruby does not allow to metaprogram false, thus something like

puts "yep" if Config.enable_stuff

always outputs yep. The workaround is to append .get, or ? to get the real value:

puts "yep" if Config.enable_stuff?

Module#===

Another thing you can't overwrite in Ruby is the === operator, rendering case statements useless

puts case Config.some.setting
     when NilClass
       "nil"
     when String
       "string"
     else
       "unknown"
     end

will always output unknown. Again use .get

Shipped providers

Configurate::Provider::Base

A convenience base class changing the interface for implementers. It provides a basic #lookup method which just passes all parameters through to #lookup_path. The result of #lookup_path is returned, unless it's nil then Configurate::SettingNotFoundError is raised. Subclasses are expected to implement #lookup_path. Do not use this class directly as a provider!

Configurate::Provider::Env

This class transforms a query string into a name for a environment variable and looks up this variable then. The conversion scheme is the following: Convert to uppercase, join path with underscores. So for example Config.foo.bar.baz would look for a environment variable named FOO_BAR_BAZ. Additionally it splits comma separated values into arrays.

This provider does not take any additional initialization parameters.

Configurate::Provider::YAML

This provider reads settings from a given YAML file. It converts the sections of query string to a nested value. For a given YAML file

stuff:
  enable: true
  param: "foo"
  nested:
    param: "bar"

the following queries would be valid:

Config.stuff.enable?      # => true
Config.stuff.param        # => "foo"
Config.stuff.nested.param # => "bar"

The initializer takes a path to the configuration file as mandatory first argument and the following optional parameters, as a hash:

• namespace: Specify a alternative root. This is useful if you for example add the same file multiple times through multiple providers, with different namespaces, letting you override settings depending on the rails environment, without duplicating common settings. Defaults to none.
• required: Whether to raise an error if the the file isn't found or, if one is given, the namespace doesn't exist in the file.

Configurate::Provider::Dynamic

A provider which stores the first additional parameter if the query string ends with an equal sign and can return it later. This is mainly useful for testing but can be useful to temporarily override stuff too. To clarify a small example:

Config.foo.bar         # => nil
Config.foo.bar = "baz"
Config.foo.bar         # => "baz"
Config.reset_dynamic!
Config.foo.bar         # => nil

Writing a provider

...should be pretty easy. For example here is the Configurate::Provider::Env provider:

class Configurate::Provider::Env < Configurate::Provider::Base
  def lookup_path(setting_path, *args)
    value = ENV[setting_path.join("_").upcase]
    unless value.nil?
      value = value.dup
      value = value.split(",") if value.include?(",")
    end
    value
  end
end

Documentation

You can find the current documentation for the master branch here.

License

MIT, see LICENSE