Handoff in iOS 8 and OS X Yosemite with Spree Commerce

add_handoff_to_orders.rb

# Generate this migration by running:
#
#     bundle exec rails g migration add_handoff_to_spree_orders handoff:string
#     bundle exec rake db:migrate
#
# db/migrate/add_handoff_to_orders.rb

class AddHandoffToOrders < ActiveRecord::Migration
  def change
    add_column :spree_orders, :handoff, :string
  end
end

base_controller_decorator.rb

# app/controllers/spree/base_controller_decorator.rb

Spree::BaseController.class_eval do

  before_action :handoff, :if => proc { params[:o].present? }

  def url_options
    return super unless current_order.present?

    { o: current_order.number }.merge(super)
  end

protected

  def handoff
    if (source = Spree::Order.find_by_number(params[:o]))
      current_order(create_order_if_necessary: true)

      if current_order.handoff != params[:o] and source.number != current_order.number
        transfer_order_contents(source, current_order)
      end
    end
  end

  def transfer_order_contents(source, destination)
    populator = Spree::OrderPopulator.new(destination, current_currency)
    destination.empty!

    source.line_items.each do |li|
      populator.populate(li.variant_id, li.quantity)
    end

    destination.ensure_updated_shipments
    destination.update_attribute(:handoff, params[:o])
  end

end