If you're using Rabl with DataMapper, lazy collection queries won't be evaluated correctly, and you'll end up SELECTing each record from the database. This patch fixes that issue (albeit, in an ugly way).

rabl_patch.rb

module Rabl

  class Engine
    def collection(data, options={})
      self.object(data_object(data))
    end
  end

  module Helpers
    def data_name(data_token)
      return unless data_token # nil or false
      return data_token.values.first if data_token.is_a?(Hash) # @user => :user
      data = data_object(data_token)
      if is_collection?(data) and data.respond_to?(:first) and not data.kind_of?(DataMapper::Collection) # data is a collection
        object_name = data_name(data.first).to_s.pluralize if data.first.present?
        object_name ||= data_token if data_token.is_a?(Symbol)
        object_name
      elsif is_object?(data) # data is an object
        object_name = object_root_name if object_root_name
        object_name ||= data if data.is_a?(Symbol)
        object_name ||= collection_root_name.to_s.singularize if collection_root_name
        object_name ||= data.class.respond_to?(:model_name) ? data.class.model_name.element : data.class.to_s.downcase
        object_name
      end
    end
  end
end