如何将参数传递给Rails中持续存在验证错误的表单？

I'm attempting to create a hierarchal menu system in rails. My menu model is in a tree data structure, and I need to pass the parent information to the new action. The best way i found to do this was to pass the parent's id as a querystring. This works, unless validation blocks creation. The problem is that after the new view is rendered, the parameter is no longer present in the url. I'm attempting to create a hierarchal menu syst