Play Framework JSON automated mapping with custom validation

Question

Hi guys I'm new in the Scala world and I want to create a simple REST API using Play Framework. I'm working on JSON mappings to Case Classes, and I have maybe a stupid question.

I have a case class that represents a UserDto (it is used for user registration, and getting some basic info about the user)

case class UserDto(id: Option[Int], email: String, username: String, password: Option[String], confirmedPassword: Option[String])

So as it says in the Play Framework docs, there are multiple ways to map this to JSON, and I'm looking at the automated mapping part

The way I've done it is

val userDtoWrites: OWrites[UserDto] = Json.writes[UserDto]
val userDtoReads: Reads[UserDto] = Json.reads[UserDto]

Now I want to add some validation to my UserDto, for example, to check if the Email is correct.

So my question is, is it somehow possible to create a Read for checking only the email field and add it to the automated generated Read?

I tried it with composeWith, but after running the second Read it only returns the email part.

val checkEmail: String = (JsPath \ "email").read[String](email)
val checkEmailJsString: JsString = checkEmail.map(s => JsString(s))
val newRead = userDtoReads.composeWith(checkEmailJsString))

For example, when a user wants to register:

{"email": "user@email.com", "username": "user","password": "password1234", "confirmedPassword": "password1234"} 

That should map to:

UserDto(None, user@email.com, user, password1234, password1234)

if everything is correct. If the password does not match or the email has a bad format is should return 400 for example.

Answer 1

If you want to have instances of UserDto which only has valid email then you should consider using Refined types (using e.g. https://github.com/avdv/play-json-refined to provide support for Play JSON).

import eu.timepit.refined._
import eu.timepit.refined.auto._
import eu.timepit.refined.api._
import play.api.libs.json._
import de.cbley.refined.play.json._

type EmailPattern = "^\S+@\S+\.\S+$"       // Scala 2.13 version
type EmailPattern = W.`"^\S+@\S+\.\S+$"`.T // before 2.13

type Email = String Refined string.MatchesRegex[EmailPattern]

case class UserDto(
  id: Option[Int],
  email: Email, // instead of plain String
  username: String,
  password: Option[String],
  confirmedPassword: Option[String]
)
object UserDto {
  implicit val userDtoWrites: OWrites[UserDto] = Json.writes[UserDto]
  implicit val userDtoReads: Reads[UserDto] = Json.reads[UserDto]
}

Answer 2

If you don't want to use another library, you can implement your own Reads[UserDto]:

case class UserDto(id: Option[Int], email: String, username: String, password: Option[String], confirmedPassword: Option[String])

implicit val reads: Reads[UserDto] = (
  (__ \ "id").readNullable[Int] and
    (__ \ "email").read[String].filter(JsonValidationError("email is not valid"))(isValid) and
    (__ \ "username").read[String] and
    (__ \ "password").readNullable[String] and
    (__ \ "confirmedPassword").readNullable[String]
  ) (UserDto).filter(
  JsonValidationError("password and confirmedPassword must be equal")
) { userDto =>
  userDto.password == userDto.confirmedPassword
}

Then you can use it:

val successfulJsonString = """{"email": "user@email.com", "username": "user", "password": "password1234", "confirmedPassword": "password1234"}"""
val emailJsonString = """{"email": "user", "username": "user","password": "password1234", "confirmedPassword": "password1234"}"""
val passwordsJsonString = """{"email": "user@email.com", "username": "user","password": "password1234", "confirmedPassword": "1234"}"""

Json.parse(successfulJsonString).validate[UserDto].fold(println, println)
Json.parse(emailJsonString).validateOpt[UserDto].fold(println, println)
Json.parse(passwordsJsonString).validate[UserDto].fold(println, println)

And get the output:

UserDto(None,user@email.com,user,Some(password1234),Some(password1234))
List((/email,List(JsonValidationError(List(email is not valid),List()))))
List((,List(JsonValidationError(List(field1 and field2 must be equal),List()))))

I took references from Scala play json combinators for validating equality and how to add custom ValidationError in Json Reads in PlayFramework to construct that solution.

Code run at Scastie.