jQuery class attribute won't change?

jQuery class attribute won't change?

Hi, when I click the link "Unapprove" an alert popup says "Ok". I want this to only happen once (as you can see, i change class name, but it doesn't work). Why ?
  1. <div class="comment">
  2.     <h3>WarzMX says:</h3>
  3.     <p>I really like jQuery, but when some error occurs I often find myself wasting hours upon hours trying to solve it, even days can go by at times. :(</p>
  4.     <p><a href="#" class="delete">Delete</a> | <a href="#" class="unapprove">Unapprove</a> | <a href="#" class="spam">Spam</a></p>
  5. </div>
jQuery:
  1. <script type="text/javascript">
  2. $(document).ready(function(){ 
  3.     $(".comment .unapprove").click(function(){
  4.         $(this).attr('class','approve');
  5.         alert('ok');
  6.     });
  7. });
  8. </script>
If I write "alert('The class attribute is now:'+$(this).attr('class'));" it gives me that class attribute is "approve". So why am I able to get into this function everytime I click??