carmen-rails is a Rails plugin that supplies two new form helper methods: country_select and subregion_select. It uses carmen as its source of geographic data.

carmen-rails requires Ruby 1.9.2 or greater.

Just add carmen-rails to your Gemfile:

gem 'carmen-rails'

<%= form_for(@order) do |f| %>
  <div class="field">
    <%= f.label :country_code %><br />
    <%= f.country_select :country_code, {priority: %w(US CA), prompt: 'Please select a country'} %>
  </div>
<% end %>

Pass the object to the country_select helper. This ensures the persisted country is selected when the form is rendered.

<%= simple_form_for @user do |f| %>
  <%= f.input :country_code do %>
    <%= f.country_select :country_code, {object: f.object, prompt: 'Country'} %>
  <% end %>
<% end %>

Passing the object is necessary when using nested form fields with Formtastic.

Carmen had a concept of excluded countries in the old days, where you could specify certain countries or regions to not include in a select.

The new (and much more flexible) way to handle this is to write a helper method that returns the subset of regions you want to provide:

def only_us_and_canada
  Carmen::Country.all.select{|c| %w{US CA}.include?(c.code)}
end

And then in your form something like this:

<%= f.select :country, region_options_for_select(only_us_and_canada) %>

Using this library will automatically set Carmen to use Rails' built-in I18n functionality. This means that changing some configuration should be done through Rails and not Carmen. For example, adding paths for additional locale files should be done inside config/application.rb:

config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s]