EF的BeginTransaction 用法

public ActionResult _Function21Update(string id)
         {
             GEN_PARAMETER parameter = db.GEN_PARAMETER.Find(id);
             if (TryUpdateModel(parameter))
             {
 
                if (ModelState.IsValid)
                 {
                     parameter.LAST_UPDATE_DATE = DateTime.Now;
                     DbConnection con = ((IObjectContextAdapter)db).ObjectContext.Connection;
                     con.Open();
                     using(var tran = con.BeginTransaction())
                     {
                         try
                         {
                             string testsql = "update test_current set value = '" + parameter.VALUE + "'";
                             db.Database.ExecuteSqlCommand(testsql);
                             db.SaveChanges();
                             //testsql = "insert1 into test_log (text) values ('code:" + parameter.CODE + "value:" + parameter.VALUE + "')";
                             testsql = "insert into test_log (text) values ('code:" + parameter.CODE + "value:" + parameter.VALUE + "')";
                             db.Database.ExecuteSqlCommand(testsql);
 
                            tran.Commit();
                         }
                         catch (Exception ex)
                         {
                             tran.Rollback();
                             db.Entry(parameter).Reload();
                             Global.Logger().Error(SysAdminErr.dbSaveErr + ex.Message, ex);
                         }
                     }
                     con.Close();
                 }
             }
             return View(new GridModel(db.GEN_PARAMETER.Where(p => p.ENABLED == "0")));
         }