Play JSON macros

This library provides helpful macros for Play JSON.

• @json adds a JSON formatter for a case class.
• @jsonFlat and JsonMacros.flatFormat creates a JSON formatter which flattens the case class with a single field to only the field value.

Inspired by json-annotation.

Setup

Add the following to your build.sbt file:

libraryDependencies += "tech.minna" %% "play-json-macros" % "1.0.1"
resolvers += Resolver.bintrayRepo("minna-technologies", "maven")

// Needed for macro annotations
addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full)

This library is compiled for both Scala 2.11 and 2.12.

Documentation

This library adds a number of annotations for automatically creating JSON formatters. This is how they work:

By using @json or @jsonFlat annotations on a case class a JSON formatter will automatically be created in the companion object.

This code:

@json case class Person(name: String, age: Int)

Will be transformed into this:

case class Person(name: String, age: Int)

object Person {
  implicit val format = Json.format[Person]
}

@json

@json case class Person(name: String, age: Int = 5)

Json.toJson(Person("Olle", 7)) == Json.obj("name" -> "Olle", "age" -> 7)

// Property `age` will be set to the default value
Json.obj("name" -> "Olle").as[Person] == Person("Olle", 5)

@json(defaultValues = false) case class Person(name: String, age: Int)

Json.toJson(Person("Olle", 7)) == Json.obj("name" -> "Olle", "age" -> 7)

// Property `age` is missing
Json.obj("name" -> "Olle").asOpt[Person] == None

@jsonFlat

@jsonFlat case class Person(name: String)

Json.toJson(Person("Olle")) == JsString("Olle")
JsString("Olle").as[Person] == Person("Olle")

JsonMacros.flatFormat

case class Person(name: String)
val format = JsonMacros.flatFormat[Person]

format.writes(Person("Olle")) == JsString("Olle")
format.reads(JsString("Olle")).get == Person("Olle")