category.rb

class Category < ActiveRecord::Base
  has_many :posts, :dependent => :destroy
  has_many :tags, :through => :posts, :uniq => true

	has_one :navigation_item, :as => :navigatable

	before_create :set_navigation_item


	private
	def set_navigation_item
		self.navigation_item = NavigationItem.new(:name => name) if navigation_item.nil?
	end
end

navigation_item_spec.rb

require "spec_helper"

describe "NavigationItem" do

	it "should have categories" do
		n = NavigationItem.new(:name => "huch", :position => 1)
		n.navigatable = Category.new(:name => "huch")
		n.save
		Category.find_by_name("huch").navigation_item.should == n
	end

	it "should have categories moep" do
		n = Category.new(:name => "huch")
		n.navigation_item = NavigationItem.new(:name => "huch", :position => 1)
		n.save
		NavigationItem.find_by_name("huch").should == n.navigation_item
	end
end