Marko.rb

class OrderItem < ActiveRecord::Base
  belongs_to :product, required: true
  belongs_to :order, required: true
  has_one :user, through: :order

  validates :quantity, presence: true, numericality: { only_integer: true, greater_than: 0 }
  validate :user_limited       
  before_save :finalize
  
  def unit_price
    if persisted?
      self[:unit_price]
    else
      product.price
    end
  end
  
  def total_price
   unit_price * quantity
  end
  
  private
        
  def finalize
   self[:unit_price] = unit_price
   self[:total_price] = quantity * self[:unit_price]
  end
  
  def user_limited
   unless user.nil? || user.allowed_to_order?
     errors.add(:user, "not allowed do more orders before #{user.new_order_date}")
  end
end


class User
  has_many :orders
  
  def allowd_to_order?
    order_count < 3 || days_since_order > 30
  end
  
  def days_since_order
    Date.today - begin_date rescue 0
  end
end

class Order
  belongs_to :user
  has_many :order_items
end