Play! Json validation that considers more than one field

Main.scala

/* This is a small example of how to use Play! Json to validate a JsValue, when you need to consider a combination
 * of fields.  In this example, I have ContactInfo, where either a phone number or an email address have to provided
 * (or both).  Each field is represented as a simple String, when in reality you may want to do further validation
 * on each field to make sure it is a valid phone number and/or email.
 */

import play.api.libs.json._

object Main {

  case class ContactInfo(phoneNumber: Option[String], email: Option[String])

  implicit object ContactInfoReads extends Reads[ContactInfo] {

    private val emailKey = "email"
    private val phoneNumberKey = "phoneNumber"

    override def reads(json: JsValue): JsResult[ContactInfo] = {

      val maybePhoneNumber = (json \ phoneNumberKey).asOpt[String]
      val maybeEmail = (json \ emailKey).asOpt[String]

      if (maybePhoneNumber.isEmpty && maybeEmail.isEmpty) {
        JsError(s"Either ${JsPath() \ phoneNumberKey} must be provided, or ${JsPath() \ emailKey} must be provided")
      }

      else {
        JsSuccess(ContactInfo(maybePhoneNumber, maybeEmail))
      }
    }
  }

  def main(args: Array[String]): Unit = {

    val test1 = Json.obj("phoneNumber" -> "1-800-123-4567").as(ContactInfoReads)
    println(test1)
    // Output: ContactInfo(Some(1-800-123-4567),None)


    val test2 = Json.obj("email" -> "[email protected]").as(ContactInfoReads)
    println(test2)
    // Output: ContactInfo(None,Some([email protected]))


    val test3 = Json.obj("phoneNumber" -> "1-800-123-4567", "email" -> "[email protected]").as(ContactInfoReads)
    println(test3)
    // Output: ContactInfo(Some(1-800-123-4567),Some([email protected]))


    val test4 = Json.obj("somethingElse" -> 991).as(ContactInfoReads)
    println(test4)
    // Output: Exception in thread "main" play.api.libs.json.JsResultException: JsResultException(errors:List((,List(ValidationError(List(Either /phoneNumber must be provided, or /email must be provided),WrappedArray())))))
  }
}