Codec

There are extension methods for Encoder, Decoder and Codec.

Encoder[A].renameFields

With renameFields, you can make the existing JSON Encoder to rename the existing fields.

import extras.circe.codecs.encoder._

Encoder[A].renameFields (
  "name1" -> "newName1",
  "name2" -> "newName2"
) // Encoder[A]

Example

import io.circe._
import io.circe.syntax._
import io.circe.generic.semiauto._
import extras.circe.codecs.encoder._

final case class Something(n: Int, s: String, price: BigDecimal)
object Something {
  implicit val somethingEncoder: Encoder[Something] =
    deriveEncoder[Something]
      .renameFields(
        "n" -> "id",
        "s" -> "name"
      )
}

val something = Something(1, "Vibranium Shield", BigDecimal(999999999))
// something: Something = Something(
//   n = 1,
//   s = "Vibranium Shield",
//   price = 999999999
// )
something.asJson
// res1: Json = JObject(
//   value = object[price -> 999999999,id -> 1,name -> "Vibranium Shield"]
// )
something.asJson.spaces2
// res2: String = """{
//   "price" : 999999999,
//   "id" : 1,
//   "name" : "Vibranium Shield"
// }"""

Comparison

Let's compare it with the Encoder without renameFields syntax.

import io.circe._
import io.circe.syntax._
import io.circe.generic.semiauto._
import extras.circe.codecs.encoder._

final case class Something(n: Int, s: String, price: BigDecimal)
object Something {
  val originalSomethingEncoder: Encoder[Something] = deriveEncoder
  implicit val somethingEncoder: Encoder[Something] = originalSomethingEncoder
    .renameFields(
      "n" -> "id",
      "s" -> "name"
    )
}

val something = Something(1, "Vibranium Shield", BigDecimal(999999999))
// something: Something = Something(
//   n = 1,
//   s = "Vibranium Shield",
//   price = 999999999
// )

Something.originalSomethingEncoder(something)
// res4: Json = JObject(
//   value = object[n -> 1,s -> "Vibranium Shield",price -> 999999999]
// )
Something.originalSomethingEncoder(something).spaces2
// res5: String = """{
//   "n" : 1,
//   "s" : "Vibranium Shield",
//   "price" : 999999999
// }"""

something.asJson
// res6: Json = JObject(
//   value = object[price -> 999999999,id -> 1,name -> "Vibranium Shield"]
// )
something.asJson.spaces2
// res7: String = """{
//   "price" : 999999999,
//   "id" : 1,
//   "name" : "Vibranium Shield"
// }"""

Decoder[A].renameFields

With renameFields, you can make the existing JSON Decoder to rename the existing fields.

import extras.circe.codecs.encoder._

Decoder[A].renameFields (
  "name1" -> "newName1",
  "name2" -> "newName2"
) // Decoder[A]

Example

import io.circe._
import io.circe.syntax._
import io.circe.generic.semiauto._
import extras.circe.codecs.decoder._

final case class Something(n: Int, s: String, price: BigDecimal)
object Something {
  implicit val somethingDecoder: Decoder[Something] =
    deriveDecoder[Something]
      .renameFields(
        "n" -> "id",
        "s" -> "name"
      )
}

val jsonString =
  """
  {
    "id": 1,
    "name": "Vibranium Shield",
    "price": 999999999
  }
  """ 
// jsonString: String = """
//   {
//     "id": 1,
//     "name": "Vibranium Shield",
//     "price": 999999999
//   }
//   """

import io.circe.parser._
decode[Something](jsonString)
// res9: Either[Error, Something] = Right(
//   value = Something(n = 1, s = "Vibranium Shield", price = 999999999)
// )

Comparison

Let's compare it with the Encoder without renameFields syntax.

import io.circe._
import io.circe.syntax._
import io.circe.generic.semiauto._
import extras.circe.codecs.decoder._

final case class Something(n: Int, s: String, price: BigDecimal)
object Something {
  val originalSomethingDecoder: Decoder[Something] = deriveDecoder
  implicit val somethingDecoder: Decoder[Something] =
    originalSomethingDecoder
      .renameFields(
        "n" -> "id",
        "s" -> "name"
      )
}

val jsonString =
  """
  {
    "id": 1,
    "name": "Vibranium Shield",
    "price": 999999999
  }
  """
// jsonString: String = """
//   {
//     "id": 1,
//     "name": "Vibranium Shield",
//     "price": 999999999
//   }
//   """

import io.circe.parser._
decode[Something](jsonString)(Something.originalSomethingDecoder)
// res11: Either[Error, Something] = Left(
//   value = DecodingFailure(Attempt to decode value on failed cursor, List(DownField(n)))
// )

decode[Something](jsonString)
// res12: Either[Error, Something] = Right(
//   value = Something(n = 1, s = "Vibranium Shield", price = 999999999)
// )

Codec[A].renameFields (Encoder + Decoder)

With renameFields, you can make the existing JSON Codec to rename the existing fields.

import extras.circe.codecs.codec._

Codec[A].renameFields (
  "name1" -> "newName1",
  "name2" -> "newName2"
) // Codec[A]

Example

import io.circe._
import io.circe.syntax._
import io.circe.generic.semiauto._
import extras.circe.codecs.codec._

final case class Something(n: Int, s: String, price: BigDecimal)
object Something {
  implicit val somethingCodec: Codec[Something] =
    deriveCodec[Something]
      .renameFields(
        "n" -> "id",
        "s" -> "name"
      )
}

val something = Something(1, "Vibranium Shield", BigDecimal(999999999))
// something: Something = Something(
//   n = 1,
//   s = "Vibranium Shield",
//   price = 999999999
// )
something.asJson
// res14: Json = JObject(
//   value = object[price -> 999999999,id -> 1,name -> "Vibranium Shield"]
// )
val jsonString = something.asJson.spaces2
// jsonString: String = """{
//   "price" : 999999999,
//   "id" : 1,
//   "name" : "Vibranium Shield"
// }"""

import io.circe.parser._
decode[Something](jsonString)
// res15: Either[Error, Something] = Right(
//   value = Something(n = 1, s = "Vibranium Shield", price = 999999999)
// )

Comparison

Let's compare it with the Encoder without renameFields syntax.

import io.circe._
import io.circe.syntax._
import io.circe.generic.semiauto._
import extras.circe.codecs.codec._

final case class Something(n: Int, s: String, price: BigDecimal)
object Something {
  val originalSomethingCodec: Codec[Something] = deriveCodec
  implicit val somethingCodec: Codec[Something] = originalSomethingCodec
    .renameFields(
      "n" -> "id",
      "s" -> "name"
    )
}

val something = Something(1, "Vibranium Shield", BigDecimal(999999999))
// something: Something = Something(
//   n = 1,
//   s = "Vibranium Shield",
//   price = 999999999
// )

Something.originalSomethingCodec(something)
// res17: Json = JObject(
//   value = object[n -> 1,s -> "Vibranium Shield",price -> 999999999]
// )
Something.originalSomethingCodec(something).spaces2
// res18: String = """{
//   "n" : 1,
//   "s" : "Vibranium Shield",
//   "price" : 999999999
// }"""

something.asJson
// res19: Json = JObject(
//   value = object[price -> 999999999,id -> 1,name -> "Vibranium Shield"]
// )
val jsonString = something.asJson.spaces2
// jsonString: String = """{
//   "price" : 999999999,
//   "id" : 1,
//   "name" : "Vibranium Shield"
// }"""

import io.circe.parser._
decode[Something](jsonString)(Something.originalSomethingCodec)
// res20: Either[Error, Something] = Left(
//   value = DecodingFailure(Attempt to decode value on failed cursor, List(DownField(n)))
// )

decode[Something](jsonString)
// res21: Either[Error, Something] = Right(
//   value = Something(n = 1, s = "Vibranium Shield", price = 999999999)
// )