Not Get the ID when edit the record in MVC 3

public ActionResult Edit(int id)
       {
           using (var db = new TestEntities())
           {
               return View(db.DepartmentMasters.Find(id));
           }
       }

       [HttpPost]
       public ActionResult Edit(int id, DepartmentMaster dm)
       {
           try
           {
               using (var db = new TestEntities())
               {
                   db.Entry(dm).State = System.Data.EntityState.Modified;
                   db.SaveChanges();
                   return RedirectToAction("Index");
               }
           }
           catch
           {
               return View();
           }
       }

Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.