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PROBLEM.1.md

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Problem #1

This gets solved by:

implicit def enc[T <: EnumEntry]: ValueEncoder[T] =
    (data: T, _: ValueCodecConfiguration) => BinaryValue( data.entryName )

implicit def schema[T <: EnumEntry]: TypedSchemaDef[T] =
  SchemaDef.primitive(
    PrimitiveType.PrimitiveTypeName.BINARY,
    Some( LogicalTypeAnnotation.enumType() ),
    required = true
  )
  .typed

Having a case class that contains an enumeration field:

case class SampleWithEnum(a: AB, b: Int)

Given that:

  • there are implicit OptionalValueEncoder[AB] and TypedSchemaDef[AB] available

..I would expect that:

  • the code compiles, and I can write out SampleWithEnum to Parquet.

Reality

Compilation error:

could not find implicit value for parameter e: com.github.mjakubowski84.parquet4s.ParquetSchemaResolver.TypedSchemaDef[Main.SampleWithEnum]

Or if taking a debugging line out - this is the real error:

Cannot write data of type Main.SampleWithEnum. Please check if there is implicit ValueEncoder available for each field and subfield of Main.SampleWithEnum.

Side walk

I'm used to Circe encoding/decoding, and there it's sufficient to provide a field's transformers. Circe can then create the right ones for aggregate classes.

Is it supposed to be the same, with parquet4s? I really don't know what to expect.

Alternate reality

If I add this:

import com.github.mjakubowski84.parquet4s.ParquetSchemaResolver._

..the error changes to:

ambiguous implicit values:
 both value stringSchema in trait PrimitiveSchemaDefs of type com.github.mjakubowski84.parquet4s.ParquetSchemaResolver.TypedSchemaDef[String]
 and value charSchema in trait PrimitiveSchemaDefs of type com.github.mjakubowski84.parquet4s.ParquetSchemaResolver.TypedSchemaDef[Char]
 match expected type com.github.mjakubowski84.parquet4s.SchemaDef
      val xx: TypedSchemaDef[SampleWithEnum] = implicitly   // "could not find implicit value for parameter e: com.github.mjakubowski84.parquet4s.ParquetSchemaResolver.TypedSchemaDef[Main.SampleWithEnum]"