Csv to Parquet - Nullable types

[MaxZ2033]

Hello!

First off, great library and very useful for my use-case of converting csv to parquet files. Thanks for all the work you put into this!

I'm currently facing one problem though and hope you can help me out:

The primitives in my parquet files need to be Nullable. I registered this delegate:

c.MapParquetType = type =>
{
    return type switch
    {
        // Ensures that chars are converted to string before they are passed to Parquet.Net.
        // Parquet.Net does not support values of type 'char'.
        not null when type == typeof(char) => typeof(string),
        // The ParquetWriter cannot handle null values of primitives.
        // Null values get converted to their default value.
        not null when type == typeof(long) => typeof(long?),
        not null when type == typeof(double) => typeof(double?),
        _ => type
    };
};

This works as expected. The problem is, that type string is then assigned to these Nullable types:

ChoETL/src/ChoETL.Parquet/ChoParquetRecordWriter.cs

Lines 253 to 254 in 566eea2

	else if (asRaw && type.IsNullableType())
	return typeof(string);

Is there a specific reason for this choice, or is there another way to enable Nullables for the Parquet writer?

(A small change in the RecordWriter code fixes this issue for me. I'll gladly create a PR if this is considered a bug and not a design choice 😉)

Thanks for your time!

[Cinchoo]

Pls raise PR. will look into it. thx