Yii Search Destroy All The Old Get Value In The Address Bar. Help Please

Dear all,

I have a webpage with the following address:

www.123.com/test?aid=1&bid=2

When I implement search in my page, my url will be changed to

www.123.com/test?Users%5Busername%5D=admin&yt0=Search

You can see that all my old GET value disappears.

How can I get my old GET value back so I still get

www.123.com/test?aid=1&bid=2&Users%5Busername%5D=admin&yt0=Search

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Attached are some codes for the search

   $user=new Users('search');
   $user->unsetAttributes(); 
   if(isset($_GET['Users']))
   $user->attributes=$_GET['Users'];