SQL bulkCopy 写入空字符串而不是 NULL

Question

我有将新值插入数据库的功能：

public async Task BulkAdd(IDataReader data)
{
    if (Connection.State == ConnectionState.Broken || Connection.State == ConnectionState.Closed)
    {
        await Connection.OpenAsync();
    }
    using (SqlBulkCopy bulk = new SqlBulkCopy(Connection))
    {
        bulk.DestinationTableName = GetTableName();
        bulk.BatchSize = BATCH_SIZE;
        bulk.BulkCopyTimeout = 0; // for infinity write 0
        bulk.EnableStreaming = true;
        await bulk.WriteToServerAsync(data);
    }
}

插入字符串按顺序生成，如下所示： ,,11111,,7,,620,7 11111,04/15/2013 00:00:00,false,Bulgaria, 然后转换为CsvDataReader：

var csvStreamReader = MapDataExtraWithHeaders(reader, clientId, dataExtraHeadersMap, delimiter, uploadDataId, dateFormat);
using (var csv = new CsvReader(csvStreamReader))
{
    csv.Configuration.BadDataFound = null;
    csv.Configuration.Delimiter = delimiter;
    

// ADDED
csv.Configuration.TypeConverterCache.AddConverter<string>(new EmptyAsNullConverter());

    var dataReader = new CsvDataReader(csv);
      csv.ReadHeader();
       if (!HeadersValid(csv.Context.HeaderRecord, DataHeaders))
             throw new CvtException(CVTExceptionCode.Import.InvalidHeaders);
   await _transactionsDataRepository.BulkAdd(dataReader);
}

我添加了空约束，例如：

alter table [dbo].[Extra] add constraint [DF_Custom] default (null) for [Custom]

但是，当我查看添加的内容时，我发现添加了空字符串而不是 NULL。怎么解决？

Answer 1

您可以编写一个自定义转换器将空转换为空：

public class EmptyAsNullConverter : CsvHelper.TypeConversion.StringConverter
{
    public override object ConvertFromString(string text, IReaderRow row, MemberMapData memberMapData)
    {
        if (string.IsNullOrEmpty(text))
            return null;
        else
            return base.ConvertFromString(text, row, memberMapData);
    }
}

感谢brandonw

使用示例：

static void Main(string[] args)
{
    var text =
        "a,b,c,e,f" + Environment.NewLine +
        "a,,c,e,f" + Environment.NewLine +
        "a,b,c,,f";
    using (var csv = new CsvReader(new StringReader(text), CultureInfo.InvariantCulture))
    {
        csv.Configuration.TypeConverterCache.AddConverter<string>(new EmptyAsNullConverter());
        while(csv.Read())
        {
            for(int i = 0; i < 5; i++)
            {
                Console.Write($"{csv.GetField<string>(i) ?? "null"}\t");
            }
            Console.WriteLine();
        }
    }
    Console.Read();
}

输出：

a       b       c       e       f
a       null    c       e       f
a       b       c       null    f

Answer 2

您可以将 CSV 绑定到类并为其编写转换器。

public class EmptyStringConverter : ConverterBase
{
    public override object StringToField(string sourceString)
    {
        if (String.IsNullOrWhiteSpace(sourceString))
            return null;
        return sourceString;
    }
}

[FieldConverter(typeof(EmptyStringConverter))]
public string MyStrField;