如何使用CsvHelper将选定的类字段写入CSV？

Question

我CsvHelper用来读取和写入CSV文件很棒,但我不明白如何只写入选定的类型字段.

说我们有:

using CsvHelper.Configuration;

namespace Project
{
    public class DataView
    {
        [CsvField(Name = "N")]
        public string ElementId { get; private set; }

        [CsvField(Name = "Quantity")]
        public double ResultQuantity { get; private set; }

        public DataView(string id, double result)
        {
            ElementId = id;
            ResultQuantity = result;
        }
    }
}

我们希望CsvField从当前生成的CSV文件中排除"数量" ,例如:

using (var myStream = saveFileDialog1.OpenFile())
{
    using (var writer = new CsvWriter(new StreamWriter(myStream)))
    {
        writer.Configuration.Delimiter = '\t';
        writer.WriteHeader(typeof(ResultView));
        _researchResults.ForEach(writer.WriteRecord);
    }
}

我可以使用什么来动态地从CSV中排除类型字段？

如果有必要,我们可以处理生成的文件,但我不知道如何删除整个CSV列CsvHelper.

Answer 1

我最近需要通过确定在运行时包含哪些字段来实现类似的结果.这是我的方法:

1. 创建一个映射文件,通过将枚举传入类构造函数来映射运行时需要的字段

   public sealed class MyClassMap : CsvClassMap<MyClass>
   {
       public MyClassMap(ClassType type)
       {
           switch (type)
           {
               case ClassType.TypeOdd
                   Map(m => m.Field1);
                   Map(m => m.Field3);
                   Map(m => m.Field5);                 
                   break;
               case ClassType.TypeEven:
                   Map(m => m.Field2);
                   Map(m => m.Field4);
                   Map(m => m.Field6);                 
                   break;
               case ClassType.TypeAll:
                   Map(m => m.Field1);
                   Map(m => m.Field2);
                   Map(m => m.Field3);
                   Map(m => m.Field4);
                   Map(m => m.Field5);
                   Map(m => m.Field6);                 
                   break;
           }
       }
   }
   

2. 使用映射配置写出记录

   using (var memoryStream = new MemoryStream())
   using (var streamWriter = new StreamWriter(memoryStream))
   using (var csvWriter = new CsvWriter(streamWriter))
   {
       csvWriter.Configuration.RegisterClassMap(new MyClassMap(ClassType.TypeOdd));
       csvWriter.WriteRecords(records);
       streamWriter.Flush();
       return memoryStream.ToArray();
   }
   

Answer 2

像这样标记字段：

[CsvField( Ignore = true )]
public double ResultQuantity { get; private set; }

更新：没关系。我看到您想在运行时执行此操作，而不是在编译时执行此操作。对于可能犯同样错误的其他人，我会将其作为危险信号。

Answer 3

你可以这样做：

using (var myStream = saveFileDialog1.OpenFile())
{
    using (var writer = new CsvWriter(new StreamWriter(myStream)))
    {
        writer.Configuration.AttributeMapping(typeof(DataView)); // Creates the CSV property mapping
        writer.Configuration.Properties.RemoveAt(1); // Removes the property at the position 1
        writer.Configuration.Delimiter = "\t";
        writer.WriteHeader(typeof(DataView));
        _researchResults.ForEach(writer.WriteRecord);
    }
}

我们将强制创建属性映射，然后对其进行修改，从而动态删除该列。

Answer 4

我的代码有类似的问题，我通过以下代码修复了它。

你可以这样做：

var ignoreQuantity = true;
using (var myStream = saveFileDialog1.OpenFile())
{
    using (var writer = new CsvWriter(new StreamWriter(myStream)))
    {
        var classMap = new DefaultClassMap<DataView>();
        classMap.AutoMap();
        classMap.Map(m => m.ResultQuantity).Ignore(ignoreQuantity)

        writer.Configuration.RegisterClassMap(classMap);

        writer.Configuration.Delimiter = "\t";
        writer.WriteHeader(typeof(DataView));
        _researchResults.ForEach(writer.WriteRecord);
    }
}