gistfile1.rb

def Restaurant.add_cuisines(restaurants)
  return [] if restaurants.empty?
  
  ids = []
  id_map = {}
  restaurants.each do |r|
    id_map[r[:id]] = r
    ids << r[:id]
    # make sure ActiveRecord won't try to load cuisines again
    r.cuisines.loaded
  end

  # make sure we load each Cuisine once
  cuisine_map = Hash.new {|h,id| h[id] = Cuisine.find(id)}

  RestaurantCuisine.find(:all,
                         :conditions => ["restaurant_id in (?)", ids]).each do |row|
    # use the association target so we don't do an insert
    id_map[row[:restaurant_id]].cuisines.target << cuisine_map[row[:cuisine_id]]
  end

  return restaurants
end