Symfony路由按ID查找，但url显示名称

I am working with Symfony2 project and there are routings like
pattern: /specialoffers/{id}/{name}.
In my web it shows like /specialoffers/15/offername. But i want to see only /specialoffers/offername. I need in controller the id of specialoffers to find it in my DB. How can i remake my router or controller action to show nice URLs?