随着撸码的时间增加，码感也会加强，今天看一个编码直觉案例吧！

案例：

需求：把查询到的数据列表生成csv文件

nuget包：CsvHelper

数据实体类：

    /// <summary>/// 商品/// </summary>public class Goods{/// <summary>/// 编号/// </summary>public uint ID{ get; set; }/// <summary>/// 名称/// </summary>public string Name{ get; set; }/// <summary>/// 规格/// </summary>public string Spec{ get; set; }/// <summary>/// 单位/// </summary>public string Unit{ get; set; }/// <summary>/// 制造商/// </summary>public string Manufacturer{ get; set; }/// <summary>/// 价格/// </summary>public decimal Price{ get; set; }/// <summary>/// 这里是为了打印数据方例重写ToString()/// </summary>public override string ToString(){return $"ID={ID},Name={Name},Unit={Unit},Spec={Spec},Price={Price},Manufacturer={Manufacturer}";}}

定义了一个csv操作的接口：

public interface ICsvHandle
{List<Goods> ReadCsv(string file);void WriteCsv(string file, List<Goods> goodses);
}

为了演示方便，Demo中的数据列表是通过Bogus产生(bogus在之前的文章中介绍过)

   static List<Goods> GoodsCreater(){var goodses = new List<Goods>();var options = new JsonSerializerOptions();options.Encoder = System.Text.Encodings.Web.JavaScriptEncoder.Create(UnicodeRanges.All);for (var i = 0; i < 100; i++){var goodsFaker = new Faker<Goods>("zh_CN").RuleFor(x => x.ID, x => x.Random.UInt()).RuleFor(x => x.Name, x => x.Random.ArrayElement(new string[]{"甲销唑注射液",
"葡萄糖注射液",
"盐水（氯化钠）",
"利巴韦林病毒唑针",
"氟康唑氯化钠注射液(康锐）",
"安痛定针",
"维生素B12针",
"硫酸阿米卡星注射液",
"氯化钠注射液（塑料瓶）",
"转移因子注射液",
"血塞通粉针",
"苦碟子注射液",
"注射用培美曲塞二钠(爱立汀)",
"左克注射液",
"维生素C注射液",
"硫酸庆大霉素注射液",
"盐酸左氧氟沙星注射液",
"蔗糖铁注射液",
"注射用青霉素钠",
"维生素B1针",
"疏血通注射液",
"胃复安盐酸甲氧氯普胺注射液",
"硫酸庆大霉素注射液",
"葡萄糖注射液50%",
"银杏达莫注射液",
"硫酸庆大霉素注射液",
"5%葡萄糖注射液",
"注射用氨曲南",})).RuleFor(x => x.Price, x => x.Random.Decimal()).RuleFor(x => x.Unit, x => x.Random.ArrayElement(new string[] { "个", "片", "瓶", "盒", "支", "克" })).RuleFor(x => x.Spec, x => x.Random.ArrayElement(new string[]{"5*20ml",
"250ml",
"1ml*10支",
"100ml:0.2g",
"2毫升*10支",
"10支",
"2ml*10.2克*10支",
"100ml",
"3毫升：2毫升*10支",
"20毫克",
"10mg*10支",
"0.5克",
"2ml:0.1g",
"0.25G*2ML",
"4万单位*10支",
"100ml*0.1g",
"1g",
"80万单位",
"2ml*10支",
"5毫克*60片",
"1ml:10mg",
"4万*2ml*10支",
"20ML*5支",
"5ml",
"2ml:40mg(4万单位)",
"250ml",
"0.5克*10支",
"5ML;17.5MG",
"2ML:0.5G*10支",})).RuleFor(x => x.Manufacturer, x => x.Random.ArrayElement(new string[]{"山东齐都药业/山西云鹏",
"侯马霸王药业/山西晋新双鹤/天津新郑/西安/贵州",
"山西临汾云鹏药业、山东齐都药业/山西银湖/石家庄四药/河南科伦",
"安徽联谊/无锡",
"扬子江药业集团",
"新乡常乐制药/山西太原药业/天津焦作/郑州",
"天津药业焦作",
"山东方明药业集团股份有限公司",
"石家庄四药有限公司",
"湖南一格制药有限公司",
"哈尔滨",
"通化华夏制药有限责任公司",
"德州德药制药有限公司",
"扬子江药业",
"山西晋新双鹤药业/新乡市新辉药业/河南润弘",
"河南辅仁怀庆堂制药/濮阳市汇元药业/新乡常乐",
"广西裕源药业、四川科伦大药厂",
"成都天台山制药有限公司",
"华北制药",
"安阳九州药业、山东方明药业/石药银湖制药",
"牡丹江友博药业有限公司",
"濮阳汇元/天津药业集团新郑",
"天津药业焦作/侯马",
"湖南科伦/焦作民康",
"贵州益佰制药股份有限公司",
"新乡市新辉药业/新乡常乐制药/濮阳市汇元药业",
"山东华鲁制药/山东齐都/山西云鹏制药/西安汉丰",
"重庆圣华曦药业",}));goodses.Add(goodsFaker.Generate());}return goodses;}

第一版：

csv文件格式是utf8

public class BasisCsvHandle : ICsvHandle
{public List<Goods> ReadCsv(string file){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var reader = new StreamReader(file))using (var csv = new CsvReader(reader, config)){var goodses = csv.GetRecords<Goods>();return goodses.ToList();}}public void WriteCsv(string file, List<Goods> goodses){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var writer = new StreamWriter(file)){using (var csv = new CsvWriter(writer, config)){csv.WriteRecords(goodses);}}}
}

后来有的客户要BOM类型的UTF8，其实就是在文件开头加上byte[] BOM = { 0xEF, 0xBB, 0xBF };这个字节数组就ok

为了适配合有无BOM和非BOM的UTF8，对接口进行了重构，增加默认属性(正好练一下接口默认属性的用法)，这种做法的好处是不打扰BasisCsvHandle的代码，当然，也可以更深层的重构ICsvHandle中的两个方法来适配是否是BOM UTF8

public interface ICsvHandle
{List<Goods> ReadCsv(string file);void WriteCsv(string file, List<Goods> goodses);private static bool _isBOM;public bool IsBOM { get => _isBOM; set => _isBOM = value; }
}

第二版：

public class StrengthenCsvHandle : ICsvHandle
{public List<Goods> ReadCsv(string file){MemoryStream memory = null;using (var reader = new FileStream(file, FileMode.OpenOrCreate, FileAccess.ReadWrite)){var bytes = new byte[reader.Length];reader.Read(bytes, 0, bytes.Length);if (((ICsvHandle)this).IsBOM){bytes = bytes.Skip(3).Take(bytes.Length - 3).ToArray();}memory = new MemoryStream(bytes);}var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var reader = new StreamReader(memory))using (var csv = new CsvReader(reader, config)){var goodses = csv.GetRecords<Goods>();return goodses.ToList();}}public void WriteCsv(string file, List<Goods> goodses){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var writer = new StreamWriter(file)){using (var csv = new CsvWriter(writer, config)){csv.WriteRecords(goodses);}}if (((ICsvHandle)this).IsBOM){//追究加BOMusing (var writer = new FileStream(file, FileMode.OpenOrCreate, FileAccess.ReadWrite)){var bytes = new byte[writer.Length];writer.Read(bytes, 0, bytes.Length);byte[] BOM = { 0xEF, 0xBB, 0xBF };var list = new List<byte>();list.AddRange(BOM);list.AddRange(bytes);writer.Position = 0;writer.Write(list.ToArray(), 0, list.Count);}}}
}

虽然能实现功能，但是觉得这样的代码太啰嗦，这里的本质就是在写数据时加上三个字节，读取数据时，少读三个字节，直觉告诉我，应该好像也许或者能有更简单的方式。

第三版：

public class PerfectCsvHandle : ICsvHandle
{public List<Goods> ReadCsv(string file){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var reader = new StreamReader(file))using (var csv = new CsvReader(reader, config)){if (((ICsvHandle)this).IsBOM){reader.BaseStream.Position = 3;}var goodses = csv.GetRecords<Goods>();return goodses.ToList();}}public void WriteCsv(string file, List<Goods> goodses){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var writer = new StreamWriter(file)){using (var csv = new CsvWriter(writer, config)){if (((ICsvHandle)this).IsBOM){byte[] BOM = { 0xEF, 0xBB, 0xBF };writer.Write(System.Text.Encoding.UTF8.GetString(BOM));}csv.WriteRecords(goodses);}}}
}