C# CSVhelper unable to write using a custom mapping

Question

I have recently moved from CSVHelper version 16.0.0 to 27.2.1. It seems to me for the CSV writer the mappings are lost as they are contained in the CSVContext now, instead of the CSVConfiguration.

I would like to use a custom Mapping to write to the CSV and not an autogenerated Mapping, is there a way to do this now?

using (StreamWriter _stream = new StreamWriter(_fileLocation))
{
  using (CsvWriter _csvWriter = new CsvWriter(_stream, CsvContext.Configuration))
  {
      _csvWriter.WriteRecords(items);
      _csvWriter.Flush();
  }
}

I added the code as context, as you can see the CSVWriter only accepts the Configuration, which no longer contains the mapping, so when I check the CSVWriter's context, there is no mapping. If I check the CSVContextitself, I do see a mapping, the custom one I made earlier.

example:

public class Foo
{
    public Guid id {get;set;}   
    public string name {get;set;}
    public DateTime created {get;set;}
}

So let's say I have the class Foo as above and I create a custom class mapping using the factory so:

private static ClassMap CreateMap()
{
    Factory _factory = new Factory();
            
    IHasMap<Foo> _mapper = _factory.CreateClassMapBuilder<Foo>();       
    
    _mapper.Map(x => x.id);
    _mapper.Map(x => x.name);       
    
    return _mapper.Build();
}

And then i register the Mapping as such:

_context.RegisterClassMap(CreateMap());

I will end up with the result:

Id,name,Date
d2e0b6d5-356c-4c34-9437-92942ee9232c,SomeName,2020-01-01

but the result I want is:

Id,name
d2e0b6d5-356c-4c34-9437-92942ee9232c,SomeName

I want to make one thing clear, this was working under version 16.0.0.0

Have you checked the documentation? The ClassMap<T> must be registered within the context, but then it should work as before. Otherwise please make a little example, containing the source class with 2 or 3 example values and the desired CSV output. — Oliver
– Oliver, Commented Dec 6, 2021 at 13:10
I have been using the RegisterClassMap method of the context. When I was using version 16.0.0.0 it was working as I wanted to (when the `RegisterClassMap~ was part of the configuration). I shall do my best to give an abstract example of what is happening with my code. — Dennis.Verweij
– Dennis.Verweij, Commented Dec 6, 2021 at 13:37

David Specht · Accepted Answer · 2021-12-06 14:19:41Z

3

RegisterClassMap moved from the Configuration to the Context. You have to register it on the CsvWriter.Context.

public static void Main(string[] args)
{    
    var config = new CsvConfiguration(CultureInfo.InvariantCulture)
    {
        // Configuration settings
    };
    
    using (CsvWriter _csvWriter = new CsvWriter(Console.Out, config))
    {
        var fooRecords = new List<Foo> { new Foo { id = new Guid("d2e0b6d5-356c-4c34-9437-92942ee9232c"), name = "SomeName", created = new DateTime(2020,1,1)} };

        _csvWriter.Context.RegisterClassMap(CreateMap());

        _csvWriter.WriteRecords(fooRecords);

        _csvWriter.Flush();
        
        Console.Read();
    }            
}

public class Foo
{
    public Guid id {get;set;}   
    public string name {get;set;}
    public DateTime created { get; set; }
}

private static ClassMap CreateMap()
{
    Factory _factory = new Factory();

    IHasMap<Foo> _mapper = _factory.CreateClassMapBuilder<Foo>();

    _mapper.Map(x => x.id);
    _mapper.Map(x => x.name);

    return _mapper.Build();
}

edited Dec 6, 2021 at 14:19

answered Dec 6, 2021 at 14:02

David Specht

9,2691 gold badge26 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Dennis.Verweij Over a year ago

thanks, I made an obvious boneheaded oversight of not doing the mapping after the initialization of the CsvWriter. It would be nice if you can include the context right away in the constructor, I don't know if there is a reason this isn't done?

David Specht Over a year ago

I believe the changes had to do either with performance or threading issues. I'm not sure if with the changes in Version 20.0.0, if it would work to be able to pass in the context. joshclose.github.io/CsvHelper/change-log/#section-32

Collectives™ on Stack Overflow

C# CSVhelper unable to write using a custom mapping

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related