Models in my app

class Category < ActiveRecord::Base
  has_many :dishes, :dependent => :destroy
end

class Dish < ActiveRecord::Base
  attr_accessible :assets_attributes
  belongs_to :category
  has_many :assets
  accepts_nested_attributes_for :assets, :allow_destroy => true
end

class Asset < ActiveRecord::Base
  belongs_to :dish
  has_attached_file :asset, :styles => { :large => "640x480", :medium => "300x300>", :thumb => "100x100>" }
end
class Category < ActiveRecor