Writing nested case classes into CSV

ScalaQL allows you to write nested case classes into CSV files. It will automatically flatten headers and rows when writing to a file.

Start by importing scalaql:

import scalaql._

// Docs classes
import scalaql.docs.Hogwarts._
import scalaql.docs.DocUtils._

// Imports for examples
import java.nio.file.Paths

For instance, assume you have the following case class:

case class FacultyDescription(name: String)

case class FacultyInfoStats(
  avgAge: Double, 
  totalGrade: Double
)
case class FacultyInfoNested(
  description: FacultyDescription, 
  stats: FacultyInfoStats)

Then with such Query:

val nestedAggregation: Query[From[Student], FacultyInfoNested] =
  select[Student]
    .groupBy(_.faculty)
    .aggregate((faculty, students) =>
      (
        students.avgBy(_.age.toDouble) &&
        students.sumBy(_.grade)
      ).map { case (avgAge, totalGrade) =>
        FacultyInfoNested(
          FacultyDescription(faculty),
          FacultyInfoStats(avgAge, totalGrade)
        )      
      }
    )
// nestedAggregation: Query[From[Student], FacultyInfoNested] = FROM(Hogwarts::Student) -> GROUP BY(String) -> AGGREGATE(MdocSession::App::FacultyInfoNested)

It will produce the following CSV file:

val studentsPath = Paths.get("docs/src/main/resources/students.csv")
// studentsPath: java.nio.file.Path = docs/src/main/resources/students.csv
val nestedPath = Paths.get("docs/target/stats_nested.csv")
// nestedPath: java.nio.file.Path = docs/target/stats_nested.csv

nestedAggregation
  .foreach(
    csv.write[FacultyInfoNested].file(nestedPath)
  )
  .run(
    from(
      csv.read[Student].file(studentsPath)
    )
  )
  
printFile(nestedPath)
// name,avgAge,totalGrade
// Gryffindor,18.333333333333332,250.9
// Slytherin,18.0,85.1
// Hufflepuff,17.0,90.1
//