Avoid Deadlock

avoid_deadlock.rb

def must_deadlock
  new_waypoints = get_new_waypoints
  order.transaction do
    order.waypoints.destroy_all
    new_waypoints.each |waypoint| do
      Order.waypoints.create!(waypoint)
    end
  end
end

def no_deadlock
  new_waypoints = get_new_waypoints.pluck(:id)
  old_waypoints = order.waypoints.all.pluck(:id)
  order.transaction do
    removed_ids = old_waypoints - new_waypoints
    order.waypoints.delete(removed_ids)
    added_ids = new_waypoints - old_waypoints
    added_ids.each |id| do
      order.waypoints.create(Waypoint.find(id))
    end
  end
end