barambani / chimney

Scala library for boilerplate-free data transformations

Chimney

Scala library for boilerplate-free data transformations.

In the daily life of a strongly-typed language's programmer sometimes it happens we need to transform an object of one type to another object which contains a number of the same or similar fields in their definitions.

case class MakeCoffee(id: Int, kind: String, addict: String)
case class CoffeeMade(id: Int, kind: String, forAddict: String, at: ZonedDateTime)

Usual approach is to just rewrite fields one by one

val command = MakeCoffee(id = Random.nextInt,
                         kind = "Espresso",
                         addict = "Piotr")
val event = CoffeeMade(id = command.id,
                       kind = command.kind,
                       forAddict = command.addict,
                       at = ZonedDateTime.now)

While the example stays lean, in real-life code we usually end up with tons of such boilerplate, especially when:

• we maintain typed schema and want to migrate between multiple schema versions
• we apply practices like DDD (Domain-Driven-Design) where suggested approach is to separate model schemas of different bounded contexts
• we use code-generation tools like Protocol Buffers that generate primitive types like Int or String, while you'd prefer to use value objects in you domain-level code to improve type-safety and readability

Chimney provides a compact DSL with which you can define transformation rules and transform your objects with as little boilerplate as possible. Underneath it uses type-level meta-programming based on Shapeless and type-class derivation to give you type-safety at compile-time!

import io.scalaland.chimney.dsl._

val event = command.into[CoffeeMade]
  .withFieldComputed(_.at, _ => ZonedDateTime.now)
  .withFieldRenamed(_.addict, _.forAddict)
  .transform

Getting started

To include Chimney to your SBT project, add the following line to your build.sbt:

libraryDependencies += "io.scalaland" %% "chimney" % "0.1.8"

Library is released for Scala 2.11 and 2.12. If you want to use it with Scala.js, you need to replace %% with %%%. Due to some compiler bugs, it's recommended to use at least Scala 2.11.9 or 2.12.1.

Documentation

Chimney documentation is available at https://scalalandio.github.io/chimney