ParquetCellConverter

Method to get the ParquetCellConverter of T: its own, if there is one; otherwise, if T is a case class, a derived one.

Method to derive a ParquetCellConverter[T] for a case class T, so that case class T(...) derives ParquetCellConverter works. This replaces the converter2 ... converter8 methods (and the reflection) of 1.x, and has no limit on the number of fields.

Each field is read from the column whose name is given by ColumnHelper[T] for that field's name. The field names come from the Mirror (at compile time), in declaration order. A field whose type is itself a case class (a "grouped" field), and which has no ParquetCellConverter of its own, is derived in turn: its fields are read from the same (flat) row, using its own ColumnHelper.

NOTE: as for CellParser.derived, don't derive the converter of a case class defined inside a method in a companion object that you write for it.

Method to create a ParquetCellConverter for a primitive column.

Converter for Option[T] fields. Returns None if the field has no value in this row, Some(value) otherwise. T must be read from a single column (an optional case class is not supported).