public bool Edit(Student sd)
        {
            Student ss = new Student();
            ss.t_id = sd.t_id;
            ss.t_sname = sd.t_sname;
            ss.t_state = sd.t_state;

           ll.ApplyCurrentValues<Student>("Student",ss)
           ll.SaveChanges();
            return true;
        }

using (var edm = new NorthwindEntities())
            {
                    Customers addc = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c2");
                    addc.City = "CD";
                    addc.ContactName = "cnblogs";
                    addc.Country = "CN";
                    int result = edm.SaveChanges();
                    Assert.AreEqual(result, 1);
                    Customers updatec = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c2");
                    Console.WriteLine("CustomerId={0},City={1}", updatec.CustomerID, updatec.City);
              }