Add MapOrdinal method to the IDataTransformer interface and provide
a default implementation in DataTransformerBase. This enables
transformers to report the mapping between transformed ordinals and
source ordinals, supporting use cases like computed columns which
return -1 to indicate no source ordinal.
- Add MapOrdinal(int, IDataReader) to IDataTransformer interface
- Add virtual MapOrdinal implementation in DataTransformerBase
- Add DataTransformerBaseTests with test for default behavior
Add core transformer infrastructure for the ETL pipeline:
- DataTransformerBase: abstract base class with virtual methods for
field count, names, types, values, ordinals, and null checking
- TransformingDataReader: IDataReader wrapper that delegates to
transformer, enabling on-the-fly data transformations
Joseph Doherty