DistroPropaganda/code/rails30/depot_q/app/models/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.
#---
#---
# Excerpted from "Agile Web Development with Rails, 4rd Ed.",
# 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
  default_scope :order => 'title'
  has_many :line_items
  has_many :orders, :through => :line_items
  #...
  before_destroy :ensure_not_referenced_by_any_line_item


  # validation stuff...
  validates :title, :description, :image_url, :presence => true
  validates :price, :numericality => {:greater_than_or_equal_to => 0.01}
# 
  validates :title, :uniqueness => true
  validates :image_url, :format => {
    :with    => %r{\.(gif|jpg|png)$}i,
    :message => 'must be a URL for GIF, JPG or PNG image.'
  }
  validates :title, :length => {:minimum => 10}
  private
    # ensure that there are no line items referencing this product
    def ensure_not_referenced_by_any_line_item
      if line_items.empty?
        return true
      else
        errors.add(:base, 'Line Items present')
        return false
      end
    end
end