title: Change object permalink length to be of the size of a predefined length
body: <p>Let´s say I have a model, called Car, and I can access my car show action at <code>/cars/:id</code>. The first record will live in <code>/cars/1</code> but I don´t want it. I want the permalink to have a length of 8 numbers, no matter what´s the id of the car. So for example, the first permalink would be  <code>00000001</code> not <code>1</code>. </p>
  
  <p>I don´t know how to implement that, what to do in the model (<code>to_param</code> method probably) or what to do in the routes.</p>
  
  <p>Please help me if you can, I appreciate any hint. </p>