linq to entity

/// <summary>
        /// 添加庄稼
        /// </summary>
        /// <param name="_UserFarm"></param>
        /// <returns></returns>
        public UserFarm AddUserFarm(UserFarm _UserFarm)
        {
                        DataContext.AddToUserFarm(_UserFarm);
            DataContext.SaveChanges();
            return _UserFarm;
        }

---------------------------------------------以上不可以是添加 ,为更新的操作.--------------

/// <summary>
        /// 添加庄稼
        /// </summary>
        /// <param name="_UserFarm"></param>
        /// <returns></returns>
        public UserFarm AddUserFarm(UserFarm _UserFarm)
        {
            UserFarm uf = new UserFarm();
            uf = _UserFarm;
            DataContext.AddToUserFarm(uf);
            DataContext.SaveChanges();
            return uf;
        }