准备项：negut包引用 CsvHelper

webapi基于IFormCollection接收文件

        var files = (FormFileCollection)formCollection.Files;
            if (files.Count == 0)
                return Failed<string>("请上传xls或者xlsx类型或者CSV的文件");
            foreach (var (file, plexus) in from IFormFile file in files
                                           let plexus = FileHelper.GetPostfixStr(file.FileName).Replace(".", "").ToLower()
                                           select (file, plexus))
            {
                if (!(plexus.Equals(FileEnum.xls.ObjToString()) || plexus.Equals(FileEnum.xlsx.ObjToString()) || plexus.Equals(FileEnum.csv.ObjToString())))
                    return Failed<string>("请上传xls或者xlsx类型或者csv类型的文件");
                var dataDtos = new List<RemittancelistDto>();
                if (plexus.Equals(FileEnum.csv.ObjToString()))
                {                  
                    var stream = file.OpenReadStream();
                    TextReader textReader = new StreamReader(stream);
                    using var csv = new CsvReader(textReader, CultureInfo.InvariantCulture);
                    csv.Read();//开始读取文件
                    csv.ReadHeader();  //读取首行记录作为表头
                    while (csv.Read())  //逐行读取
                    {
                        var record = new RemittancelistDto
                        {           
                            OrderNo = csv.GetField("Order No."),//Excel中的字段名
                            OrderItemNo = csv.GetField("Order Item No."),             
                        };
                        dataDtos.Add(record);
                    }
                }
             }