Creates or set @order

application_controller.rb

  before_action :set_order

  def set_order
    if session[:order_id]
      @order = Order.find(session[:order_id])
    else
      @order = Order.new
    end
  end

  def create_order
    unless session[:order_id]
      @order = Order.create
      session[:order_id] = @order.id
    end
  end