[Feature request] Support for flattening models

[holinov]

It would be great to have possibility to map inner fields of object to top level object.

// Source classes
case class InnerData(name: String, ival: Int)
case class DataHolder(v: Int, data: InnerData)
case class OtherDataHolder(v: Int, data: InnerData)

// Target class
case class Target(v: Int, name: String, ival: Int)

It would be nice to have any way to tell transformer that i need to extract fields from inner classes
Now i'm using workaround like this

object InnerData {
  implicit val intoNameString: Transformer[InnerData, String] = _.name
  implicit val intoIntVal: Transformer[InnerData, Int] = _.ival
}

val data = DataHolder(1, InnerData("name_val", 10))
data
      .into[Target]
      .withFieldRenamed(_.data, _.name)
      .withFieldRenamed(_.data, _.ival)
      .transform

Main problem here is that i have no possibility to reuse it on OtherDataHolder so i need every time to write this code.

[REDNBLACK]

Yeah, would be even better if it supported shapeless.Witness selector for fieldFrom/fieldTo names, like this:

LabelledTransformer[FieldFrom <: Symbol, FieldTo <: Symbol, From, To]

object InnerData {
  implicit val intoNameString: LabelledTransformer[W.`'data`.T, W.`'name`.T, InnerData, String] = _.name
  implicit val intoIntVal: LabelledTransformer[W.`'data`.T, W.`'ival`.T, InnerData, Int] = _.ival
}

[krzemin]

One of possible solutions to this problem would be to allow pulling fields from nested case classes and pushing them down to nested.

DataHolder(1, InnerData("name_val", 10))
  .into[Target]
  .withFieldsPulledFrom(_.data)
  .transform
 
Target(1, "name_val", 10)
  .into[DataHolder]
  .withFieldsPushedTo(_.data, _.name, _.ival)
  .transform

It could work as long as pulling/pushing fields doesn't introduce name clash.

Other possibility is to generalize renaming to support renaming of nested fields as well:

DataHolder(1, InnerData("name_val", 10))
  .into[Target]
  .withFieldRenamed(_.data.name, _.name)
  .withFieldRenamed(_.data.ival, _.ival)
  .transform

Target(1, "name_val", 10)
  .into[DataHolder]
  .withFieldRenamed(_.name, _.data.name)
  .withFieldRenamed(_.ival, _.data.ival)
  .transform

Actually, both proposals are orthogonal and can be implemented independently.

[holinov]

as for my purposes 2nd way is ok

[holinov]

great thx