iam using ruby on rails i have models -category -subcategory -city -firm when i click on category it will show sub categories and permalink should be: xxx.com/category when i click subcategory it will show firms and city names. xxx.xom/category/subcategory when i clikc on city name it will filter firms belongs to that city xxx.com/category/subcategory/city when i clikc on firm name it will show xxx.com/category/subcategory/city/firm-name firms may have more than one sub category i used premalink_fu but i could not do that sub category system. category,subcategory,city,firm tables have their own permalink field on db. but i dont know how to combine them dynamically. i can do xxx.com/category but icant do xxx.com/category/subcategory how can i do that please help me