gistfile1.rb

require 'sunspot'
require 'mongoid'
require 'sunspot/rails'

class Post
  include Mongoid::Document
  field :title
  include Sunspot::Mongoid
  searchable do
    text :title
  end
end

# lib/sunspot/mongoid.rb

# module Sunspot
module Mongoid
  def self.included(base)
    base.class_eval do
      extend Sunspot::Rails::Searchable::ActsAsMethods
      Sunspot::Adapters::DataAccessor.register(DataAccessor, base)
      Sunspot::Adapters::InstanceAdapter.register(InstanceAdapter, base)
    end
  end

  class InstanceAdapter < Sunspot::Adapters::InstanceAdapter
    def id
      @instance.id.to_s
    end
  end

  class DataAccessor < Sunspot::Adapters::DataAccessor
    def load(id)
      @clazz.criteria.for_ids(Moped::BSON::ObjectId(id))
    end

    def load_all(ids)
      @clazz.criteria.in(:_id => ids.map {|id| Moped::BSON::ObjectId(id)})
    end
    private
    def criteria(id)
      @clazz.criteria.id(id)
    end
  end
end