UserInfo user = from u in context.UserInfo where u.Id=343 select u;

context.UserInfo.Remove(user);

 用Remove（）方法时，必须先从EF中查到才能删除

UserInfo user = new UserInfo(){Id=343};

context.Entry<UserInfo>(user).State = System.Data.EntityState.Deleted;

用这种方法不用先查再删除，其实内部做了查询，推荐用这种；