Csv Reader 可以根据列数使用不同的记录类型映射吗？

Question

我有一堆 CSV 文件需要阅读，除了添加了一列外，它们都很相似。本质上，旧的 CSV 格式有 7 列，而新的将有 8 列。没有 headers。读取后，新列将是 defaulted/edited，然后文件在写出时将有 8 列 - 因此以后的读取现在将具有新列。

所以我正在尝试做类似这个 CvsHelper 示例的事情： Reading Multiple Record Types

唯一的区别在于文件中的列数 - 而不是标识字段值。

我在自己的 using() 中尝试了一个 CsvParser，并在文件的第一行中使用了一个 Read() 来确定列数，因为随后的 using() 中的 CsvReader 可以注册一个特定的计数ClassMap 为 CsvReader.GetRecords。但是，似乎没有属性或方法可以回答解析器遇到的列数。与 CsvReader.Read() 相同 - CsvReader.Context.ColumnCount 在 Read() 之后为零。任何想法/指示表示赞赏。

更新

这是我修改后的代码（长名称，我知道）- 感谢大卫的建议：

namespace TopazDomain.Classes
{
    public class FootprintComponentMap : Entity<int>
    {
        private const int footprintWidth = 40;
        [StringLength(footprintWidth)]
        public string Footprint { get; set; }

        private const int valueWidth = 40;
        [StringLength(valueWidth)]
        public string Value { get; set; }

        public int Component { get; set; }

        public int Head { get; set; }

        private const int rotationWidth = 9;
        [StringLength(rotationWidth)]
        public string CompR { get; set; }

        private const int polarizedWidth = 2;
        [StringLength(polarizedWidth)]
        public string Polarized { get; set; }

        private const int commentWidth = 40;
        public string Comment { get; set; }

        [StringLength(rotationWidth)]
        public string LibR { get; set; }

        // navigation
        [Required]
        public FootprintComponentMapFile FootprintComponentMapFile { get; set; }

        public FootprintComponentMap()
        {
            Footprint = String.Empty;
            Value = String.Empty;
            Component = 0;
            Head = 0;
            CompR = "0.00";
            Polarized = "N";
            Comment = String.Empty;
            LibR = "0.00";
        }

        public FootprintComponentMap(FootprintComponentMap footprintComponentMap) : this()
        {
            Footprint = footprintComponentMap.Footprint;
            Value = footprintComponentMap.Value;
            Component = footprintComponentMap.Component;
            Head = footprintComponentMap.Head;
            CompR = footprintComponentMap.CompR;
            Polarized = footprintComponentMap.Polarized;
            Comment = footprintComponentMap.Comment;
            LibR = footprintComponentMap.LibR;
        }

        public FootprintComponentMap(string footprint, string value, int componentNumber, int headNumber, string componentR,
            string polarized, string libraryR, string comment) : this()
        {
            Footprint = footprint;
            Value = value;
            Component = componentNumber;
            Head = headNumber;
            CompR = componentR;
            Polarized = polarized;
            Comment = comment;
            LibR = libraryR;
        }
    }
}

namespace TopazDomain.Classes.Extensions
{
    public static class FootprintComponentMapFileExtensions
    {
        public sealed class FootprintComponentReadMapper : ClassMap<FootprintComponentMap>
        {
            public FootprintComponentReadMapper()
            {
                Map(m => m.Footprint).Index(0);
                Map(m => m.Value).Index(1);
                Map(m => m.Component).Index(2);
                Map(m => m.Head).Index(3);
                Map(m => m.CompR).Index(4);
                Map(m => m.Polarized).Index(5);
                Map(m => m.Comment).Index(6);
                Map(m => m.LibR).ConvertUsing(row =>
                {
                    if (row.TryGetField(7, out string field))
                    {
                        return field;
                    }
                    else
                    {
                        return String.Empty;
                    }
                });
            }
        }

        public sealed class FootprintComponentWriteMapper : ClassMap<FootprintComponentMap>
        {
            public FootprintComponentWriteMapper()
            {
                Map(m => m.Footprint).Index(0);
                Map(m => m.Value).Index(1);
                Map(m => m.Component).Index(2);
                Map(m => m.Head).Index(3);
                Map(m => m.CompR).Index(4);
                Map(m => m.Polarized).Index(5);
                Map(m => m.Comment).Index(6);
                Map(m => m.LibR).Index(7);
            }
        }

        public static bool ImportFootprintComponentMaps(this FootprintComponentMapFile footprintComponentMapFile,
            string filename)
        {
            bool done = false;

            using (var lineReader = new LineReader(filename))
            using (var csv = new CsvReader(lineReader, CultureInfo.InvariantCulture))
            {
                csv.Configuration.RegisterClassMap<FootprintComponentReadMapper>();

                footprintComponentMapFile.FootprintComponentMaps = csv.GetRecords<FootprintComponentMap>().ToList();

                done = true;
            }

            return done;
        }

        public static bool ExportFootprintComponentMaps(this FootprintComponentMapFile footprintComponentMapFile,
            string filename)
        {
            bool done = false;

            CsvConfiguration cvsConfiguration = new CsvConfiguration(CultureInfo.InvariantCulture);
            cvsConfiguration.HasHeaderRecord = false;

            using (var lineWriter = new StreamWriter(filename))
            using (var csv = new CsvWriter(lineWriter, cvsConfiguration))
            {
                csv.Configuration.RegisterClassMap<FootprintComponentWriteMapper>();

                csv.WriteRecords(footprintComponentMapFile.FootprintComponentMaps);

                done = true;
            }

            return done;
        }
    }
}

Answer 1

您可以创建一个具有 8 个属性的新对象，并使用 ConvertUsing 有条件地映射第 8 列。

public class OldFoo
{
    public int Id { get; set; }
    public string FirstName { get; set; }
}

public class NewFoo 
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

public class NewFooClassMap : ClassMap<NewFoo>
{
    public NewFooClassMap()
    {
        Map(m => m.Id).Index(0);
        Map(m => m.FirstName).Index(1);
        Map(m => m.LastName).ConvertUsing(row => {                
            if(row.TryGetField(2, out string field))
            {
                return field;
            }
            else
            {
                return null;
            }
        });
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        using (MemoryStream stream = new MemoryStream())
        using (StreamWriter writer = new StreamWriter(stream))
        using (StreamReader reader = new StreamReader(stream))
        using (CsvReader csv = new CsvReader(reader, CultureInfo.InvariantCulture))
        {
            writer.WriteLine("1,Bob");
            writer.WriteLine("2,Davey");
            writer.Flush();
            stream.Position = 0;

            csv.Configuration.RegisterClassMap<NewFooClassMap>();
            csv.Configuration.HasHeaderRecord = false;

            var records = csv.GetRecords<NewFoo>().ToList();

        }

        using (MemoryStream stream = new MemoryStream())
        using (StreamWriter writer = new StreamWriter(stream))
        using (StreamReader reader = new StreamReader(stream))
        using (CsvReader csv = new CsvReader(reader, CultureInfo.InvariantCulture))
        {
            writer.WriteLine("1,Bob,Barker");
            writer.WriteLine("2,Davey,Jones");
            writer.Flush();
            stream.Position = 0;

            csv.Configuration.RegisterClassMap<NewFooClassMap>();
            csv.Configuration.HasHeaderRecord = false;

            var records = csv.GetRecords<NewFoo>().ToList();

        }
    }
}

Csv Reader 可以根据列数使用不同的记录类型映射吗？

Can CsvReader use different Record Type Maps based upon column count?

csvhelper

csvreader