novelty.rb

class Novelty < ActiveRecord::Base
  
  attr_accessible         :body, :photo, :title  
  has_and_belongs_to_many :topics

  has_attached_file :photo,
                    :styles => { :thumb=> "100x100#",:small  => "150x150>" },
                    :url   => "/uploads/images/:class/:attachment/:id/:style/:basename.:extension",
                    :path  => ":rails_root/public/uploads/images/:class/:attachment/:id/:style/:basename.:extension"
                 
  validates_attachment_content_type :photo,:content_type => ['image/jpeg','image/gif' ] unless #Aqui necesito preguntar si hay imagen o no

  validates_attachment_size :photo , :less_than => 3.megabytes unless  #Aqui necesito preguntar si hay imagen o no
  validates_presence_of     :body  , :title

end