How can I upsert a bunch of ActiveRecord objects and relationships in Rails?

# routes is an array of [number, destination] that I build while iterating over the data
routes.uniq.each do |route|
  number      = route[0]
  destination = route[1]

  r = Route.find_by_number_and_destination(number, destination)

  if !r
    r = Route.new :number => number, :destination => destination
    r.save
  end

  # I have to check if it already exists because I can't find a way
  # to create a uniqueness constraint on the join table with 2 foreign keys
  r.stops << stop unless r.stops.include? stop
end

class Route < ActiveRecord::Base
  has_and_belongs_to_many :stops
  belongs_to :stop, :foreign_key => 'destination_id'
end

class Stop < ActiveRecorde::Base
  has_and_belongs_to_many :routes
end

create_table :routes do |t|
  t.integer :destination_id
  # Any other information you want to store about routes
end

create_table :stops do |t|
  # Any other information you want to store about stops
end

create_table :routes_stops, :primary_key => [:route_id, :stop_id] do |t|
  t.integer :route_id
  t.integer :stop_id
end

# First, find all the relevant routes, just for caching.
Route.find(numbers)

r = Route.find(number)
r.destination_id = destination
r.stops << stop