public Task<Result<IEnumerable<Res_Course>>> GetCourses() {
            try {
                var x = new Result<IEnumerable<Res_Course>> { Message = "添加课程成功", Success = true };
                x.Content =dblm.Res_Course;//.ToArray();
                return Task.FromResult(x);
            } catch (Exception e) {
                var x = new Result<IEnumerable<Res_Course>> { Message = e.Message, Success = false };
                return Task.FromResult(x);
            }
        }