Especially if you have multiple API templates or models with many fields, it's a good idea to put your API template definitions in their own file. Here is a possible solution:

First create a directory /app/representations/api_v1. This is were we will keep our API templates.

Now add the following line in your application configuration in the /config/application.rb file:

config.autoload_paths += %W(#{config.root}/app/representations)

Given we have a model named User we will now create the file /app/representations/api_v1/user.rb where we define the API templates for the User model:

module ApiV1::User
  extend ActiveSupport::Concern
  included do
    api_accessible :name_only do |t|
      t.add :first_name
    end
  end
end

In the User model itself we just include the module:

class User < ActiveRecord::Base
  
  acts_as_api
  include ApiV1::User
  
end

That's it! :)