Domain, API, DTO

Translating between layers with Chimney

Mateusz Kubuszok

About me

breaking things in Scala for 9 years
a little bit of open source - including co-authoring Chimney for almost 7 years now
blog at Kubuszok.com
niche Things you need to know about JVM (that matter in Scala) ebook

Once upon a time

simple web backend
Circe codecs
Doobie (well, Slick actually)
Protobuf and Kinesis (well, it was Avro and Postgres)

Let’s look at example

It kinds works, but let add a few modifications:

for creationDate let’s use Instant`
for id let’s use UUID

We can still improve it!

let’s create a separate model for JSONs
let’s create a separate model for DB operations

Could we get rid of the silly code for mapping?

YES

What is possible with Chimney?

case class to case class

case class Source(a: Int, b: String, c: Boolean)
case class Target(b: String, a: Int)

import io.scalaland.chimney.dsl.*
Source(777, "value", c = true).transformInto[Target]
// Target("value", 777)

case class Source(a: Int, b: String)
case class Target2(b: String, a: Int, extra: Double)

import io.scalaland.chimney.dsl.*
Source(777, "value").into[Target2]
  .withFieldConst(_.extra, 3.14)
  .transform // Target2("value", 777, 3.14)
Source(777, "value").into[Target2]
  .withFieldComputed(_.extra, src => src.a.toDouble)
  .transform // Target2("value", 777, 777.0)

ADT to ADT

enum Source:
  case Foo, Bar(b: Int)
enum Target:
  case Foo, Bar(b: Int), Baz

import io.scalaland.chimney.dsl.*
(Source.Bar(777): Source).transformInto[Target]
// Target.Bar(777)

enum Source:
  case Foo, Bar(b: Int), Baz
enum Target:
  case Foo, Bar(b: Int)

import io.scalaland.chimney.dsl.*
(Source.Baz: Source).into[Target]
  .withEnumCaseHandled[Source.Baz](_ => Target.Foo)
  .transform // Target.Foo

Collections

case class Source(a: Int, b: String, c: Boolean)
case class Target(b: String, a: Int)

import io.scalaland.chimney.dsl.*
List(Source(777, "value")).transformInto[Vector[Target]]
// Vector(Target("value", 777))

case class Source(a: Int, b: String)
case class Target2(b: String, a: Int, extra: Double)

import io.scalaland.chimney.dsl.*
List(Source(777, "value")).into[Vector[Target]]
  .withFieldConst(_.eachItem.extra, 3.14)
  .transform // Vector(Target("value", 777, 3.14))

More info

Thank you !