gistfile1.rb

require 'rubygems'
require 'mongo_mapper'

class User
  include MongoMapper::Document
  has_many :tweets

  key :screen_name, String, :required => true
end

class Tweet
  include MongoMapper::Document
  belongs_to :user
  key :user_id, :index => true
  
  key :status_id, Integer, :index => true, :unique => true
  key :text, String
end

MongoMapper.database = '__dpc__rm_idtest'
MongoMapper.ensure_indexes!

u = User.create(:screen_name => 'dacort')
Tweet.create(:status_id => (rand*100000).to_i, :user => u, :text => "Heyo")

Tweet.all(:user => u)
Tweet.all(:user_id => u.id)
Tweet.all(:user_id => u._id)