[Entity Framework]获取部分字段的查询

using (var ObjectContext = new AgentSystemEntities())
            {
                DateTime dt = new DateTime(1997, 1, 1);
                string entitySQL = "SELECT VALUE Users FROM Users WHERE Users.AddDateTime > @dt;";
                ObjectParameter[] ps = { new ObjectParameter("dt", dt) };
                ObjectQuery<Users> query = ObjectContext.CreateQuery<Users>(entitySQL,ps);
                string message = "执行的语句:" + query.CommandText + "\n\r";
                if (query.Count() > 0)
                {
                    message += query.First().UserNames + "\n\r";
                }
                else
                {
                    message += "没有数据\n\r";
                }
                MessageBox.Show(message);
            }