dm-test.rb

gistfile1.rb

require 'rubygems'
require 'dm-core'
require 'dm-migrations'

DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, 'postgres://localhost/test') # createdb test

class User
  include DataMapper::Resource

  property :id, Serial

  has 1, :user_profile

  def self.ranked
    order = DataMapper::Query::Direction.new(user_profile.ranking, :desc) 
    query = all.query # Access a blank query object for us to manipulate
    query.instance_variable_set("@order", [order])

    # Force the user_profile model to be joined into the query
    query.instance_variable_set("@links", [relationships['user_profile'].inverse])

    all(query) # Create a new collection with the modified query
  end
end

class UserProfile
  include DataMapper::Resource

  property :user_id, Integer, :key => true
  property :ranking, Integer, :default => 0

  belongs_to :user
end

DataMapper.finalize
DataMapper.auto_migrate!

User.create(:user_profile => UserProfile.new(:ranking => 2))
User.create(:user_profile => UserProfile.new(:ranking => 5))
User.create(:user_profile => UserProfile.new(:ranking => 3))

puts User.ranked.all(:limit => 1).map {|x| x.user_profile.ranking }.inspect