Rials, Validates form "Agile Web Development with Rails 3.2"

product.rb

#---
# Excerpted from "Agile Web Development with Rails",
# published by The Pragmatic Bookshelf.
# Copyrights apply to this code. It may not be used to create training material, 
# courses, books, articles, and the like. Contact us if you are in doubt.
# We make no guarantees that this code is fit for any purpose. 
# Visit http://www.pragmaticprogrammer.com/titles/rails4 for more book information.
#---
class Product < ActiveRecord::Base
  validates :title, :description, :image_url, presence: true
  validates :price, numericality: {greater_than_or_equal_to: 0.01}
# 
  validates :title, uniqueness: true
  validates :image_url, allow_blank: true, format: {
    with:    %r{\.(gif|jpg|png)$}i,
    message: 'must be a URL for GIF, JPG or PNG image.'
  }
end