Deserialize JSON based on Field in Payload in Scala

Question

I have a similar question with Deserialize json based on fields in .Net (C#), but do it in Scala.

I have an app which streams in 2 types of json objects (Account and User).

Account:

{
  "data_type": "account",
  "id": 1,
  "type": "Trial",
  "created_at": 1523982003,
}

User:

{
  "data_type": "user",
  "id": 1,
  "account_id": 1,
  "department": "Finance"
  "created_at": 1523982122
}

I need to deserialize the two above json objects based on the field data_type in Scala with help of Circe library.

How can I do this?

Answer 1

This snippet works for me in Ammonite:

import $ivy.`io.circe:circe-core_2.12:0.9.3`, io.circe._
import $ivy.`io.circe:circe-generic_2.12:0.9.3`, io.circe.generic._
import $ivy.`io.circe:circe-generic-extras_2.12:0.9.3`, io.circe.generic.extras._
interp.load.plugin.ivy("org.scalamacros" % "paradise_2.12.4" % "2.1.1")

implicit val config: Configuration = Configuration.
  default.
  withSnakeCaseMemberNames.
  withDiscriminator("data_type").
  copy(transformConstructorNames = _.toLowerCase)

{
@ConfiguredJsonCodec
sealed trait InputEntity
object InputEntity {
  @ConfiguredJsonCodec case class Account(id: Long, `type`: String, createdAt: Long) extends InputEntity
  @ConfiguredJsonCodec case class User(id: Long, accountId: Long, department: String, createdAt: Long) extends InputEntity
}
} 

import $ivy.`io.circe:circe-parser_2.12:0.9.3`, io.circe.parser._


val accountJson = """
{
  "data_type": "account",
  "id": 1,
  "type": "Trial",
  "created_at": 1523982003
}
"""
val account = decode[InputEntity](accountJson)
// account: Either[Error, InputEntity] = Right(Account(1L, "Trial", 1523982003L)

val userJson = """
{
  "data_type": "user",
  "id": 1,
  "account_id": 1,
  "department": "Finance",
  "created_at": 1523982122
}
"""
val user = decode[InputEntity](userJson)
// user: Either[Error, InputEntity] = Right(User(1L, 1L, "Finance", 1523982122L))

(BTW: you had syntax errors in your JSON examples that would make the parser fail, so I fixed them in code above).

The most important here is

• Configuration from io.circe.generic.extras._ that defines discriminator field,
• keeping classes as sum type,
• if you use annotations for generating codecs replace @JsonCodec with @ConfiguredJsonCodec.

Actually, you could also replace these Strings with enums, and read createdAt as LocalDateTime or similar, but that would be out of scope of this question.