Order model

gistfile1.txt

class Order < ActiveRecord::Base
  attr_accessible :client_id, :order_total, :delivery_date
  has_many :orderedproducts
  has_many :products, through: :orderedproducts, :source => :product
  has_one :client
  
  before_save :generate_total

  def generate_total
    self.order_total = self.products.sum(:product_price)
  end
end