使用CsvHelper可以将空格转换为可空吗？

Question

我有一些非常蹩脚的Csv文件我需要解析.我正在使用CsvHelper,它工作得很棒.除了我有一些行有空格的地方,我有一个双倍的正常.

文件:

文本,SomeDouble,MoreText

"好",1.23 "好"

"坏","坏"

如果我尝试将其映射到

public class Test
{
  [CsvField(Name = "Text")]
  public string Text { get; set; }

  [CsvField(Name = "SomeDouble")]
  public double? SomeDouble{ get; set; }

  [CsvField(Name = "MoreText")]
  public string MoreText{ get; set; }
}

然后我得到这样的错误:

CsvHelper.CsvReaderException:尝试读取类型记录时发生错误

行:'2'(从1开始)

场指数:'1'(基于0)

字段名称:'SomeDouble'

场地价值:''

System.Exception:不是Double的有效值.---> System.FormatException:输入字符串的格式不正确.
处于System.ComponentModel.DoubleConverter.FromString(String value,NumberFormatInfo formatInfo)的System.Number.ParseDouble(String value,NumberStyles options,NumberFormatInfo numfmt),位于System.ComponentModel.BaseNumberConverter.ConvertFrom(ITypeDescriptorContext context,CultureInfo culture,Object value) - - 内部异常堆栈跟踪的结束---在lambda_method的System.ComponentModel.NullableConverter.ConvertFrom(ITypeDescriptorContext context,CultureInfo culture,Object value)处的System.ComponentModel.BaseNumberConverter.ConvertFrom(ITypeDescriptorContext context,CultureInfo culture,Object value)处闭包,ICsvReader)在CsvHelper.CsvReader.d__0`1.MoveNext()

在我看来,我的选择是创建一个自定义解析器,或将我的值映射到字符串属性并在那里进行解析.

还有其他选择吗？

如果我可以配置我想将空格视为空,那将是很好的.

根据要求,这是一个重现问题的代码示例

 static class Program
    {
        public class Test
        {
            [CsvField(Name = "Text")]
            public string Text { get; set; }

            [CsvField(Name = "SomeDouble")]
            public double? SomeDouble { get; set; }

            [CsvField(Name = "MoreText")]
            public string MoreText { get; set; }
        }

        static void Main(string[] args)
        {
            // create fake in memory file
            var memoryStream = new MemoryStream();
            var streamWriter = new StreamWriter(memoryStream);
            streamWriter.WriteLine("Text,SomeDouble,MoreText");
            streamWriter.WriteLine("Good, 1.23, Good");
            streamWriter.WriteLine("Bad, ,Bad");

            streamWriter.Flush();

            //reset the file to the begining
            memoryStream.Position = 0;

            using (
                var csv =
                    new CsvReader(
                        new StreamReader(memoryStream)))
            {
                // this call will blow up with the exception.
                var records = csv.GetRecords<Test>().ToList();

                //carry on and do stuff with 'records'...
            }
    }

谢谢.

Answer 1

最后,我创建了自己的类型转换器,将空白与null相同.

public class WhiteSpaceToNullableTypeConverter<T> : TypeConverter where T : struct
{
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        return sourceType == typeof (string);
    }

    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
    {
        return destinationType == typeof (T?);
    }

    public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture,
                                       object value)
    {
        T? result = null;

        var stringValue = (string) value;
        if (!string.IsNullOrWhiteSpace(stringValue))
        {
            var converter = TypeDescriptor.GetConverter(typeof(T));
            result = (T)converter.ConvertFrom(stringValue.Trim());
        }

        return result;
    }

    public override object ConvertTo(ITypeDescriptorContext context, System.Globalization.CultureInfo culture,
                                     object value, Type destinationType)
    {
        var result = (T?) value;
        return result.ToString();
    }
}

像这样将它应用到您的模型中

public class Test
{
    [CsvField(Name = "Text")]
    public string Text { get; set; }

    [CsvField(Name = "SomeDouble")]
    [TypeConverter( typeof( WhiteSpaceToNullableTypeConverter<Double> ) )]
    public double? SomeDouble{ get; set; }

    [CsvField(Name = "MoreText")]
    public string MoreText{ get; set; }
}

Answer 2

一种简单的方法是在ClassMap中使用ConvertUsing():

Map(x => x.SomeDouble)
    .ConvertUsing(row => 
        string.IsNullOrWhiteSpace(row.GetField("SomeDouble")) ?
            (double?) null : 
            Convert.ToDouble(row.GetField("SomeDouble")));

我喜欢制作小辅助函数并调用它们

Map(x => x.SomeDouble)
    .ConvertUsing(row => GetOddballDouble(row.GetField("SomeDouble")));