photo.rb

require 'securerandom'
class Photo < ActiveRecord::Base
  validates :title, presence: true
  validates :photo, presence: true
  before_create :rename_photo
  has_many :comments

  has_attached_file :photo,
      :path => ":rails_root/public/uploads/:class/:attachment/:id/:style/:basename.:extension",
      :url => '/i/:basename.:extension',
      :styles => {:medium => "500x500>", :thumb => "100x100>"}

  validates_attachment_content_type :photo, :content_type => /\Aimage\/.*\Z/

  belongs_to :user

  def rename_photo
    extension = File.extname(photo_file_name).downcase
    self.photo.instance_write :file_name, "#{SecureRandom.urlsafe_base64(10)}#{extension}"
  end
end