Check or find if a particular path exists in json using play framework and scala

Question

I am trying to parse a json using play framework into a case class. My intention here is to check whether a particular path exists in the json. If exists then only read element at that path.

Here is my code

package com.learning.avinash.query

import play.api.libs.json.{JsDefined, JsPath, Json, Reads, Writes, __}
import play.api.libs.functional.syntax._

object ParseJson extends App {

  case class Msisdn(primaryId: Option[String], relatedAccountId: Option[String])

  object Msisdn {
    implicit val readData: Reads[Msisdn] = (
      (JsPath \ "primary-id").readNullable[String] ~
      (JsPath \ "meta" \ "related-account-id").readNullable[String]
      ) (Msisdn.apply _)
  }



val testJson = """{
  "resources": [
    {
    "valid-for-start-datetime": "2019-08-23T10:47:17.485Z",
    "primary-id": "393823468684",
      "meta": {
        "related-account-id": "10001771",
            "roles": [
              "customer"
            ]
        }
    },
  {
    "valid-for-start-datetime": "2019-08-23T10:47:17.485Z",
    "primary-id": "393823467689"
    }
  ]
}"""
    println((Json.parse(testJson) \ "resources").as[List[Msisdn]])
}

In the resources array in the second object you can observe this code is completely missing

"meta": {
            "related-account-id": "10001771",
                "roles": [
                  "customer"
                ]
            }

Now when i try to parse the json, it fails and i get the following exception

Exception in thread "main" play.api.libs.json.JsResultException: JsResultException(errors:List(((1)/meta/related-accoount-id,List(JsonValidationError(List(error.path.missing),WrappedArray())))))

Is there a predefined function/method in play so that i can check whether this

(JsPath \ "meta")

particular path exists and then only read the element in that path. Or should i write a custom function to check whether the path exists.

I could see a JsDefined() which expects a Jsvalue.

https://www.playframework.com/documentation/2.7.x/api/scala/play/api/libs/json/index.html

final case classJsDefined(value: JsValue)
Wrapper for JsValue to represent an existing Json value.

Any thoughts, ideas, help or suggestions please.

there is grammar error in accoount (related-accoount-id). It is not reason of exception, of course — Mikhail Ionkin
– Mikhail Ionkin, Commented Dec 10, 2019 at 21:29

Mikhail Ionkin · Accepted Answer · 2019-12-10 21:37:33Z

2

May be it will be helpful...

1-st way is use Json.format:

import play.api.libs.json._

object ParseJson extends App {

  case class Msisdn(`primary-id`: Option[String], meta: Option[Meta])
  case class Meta(`related-account-id`: Option[String])
  implicit val metaFormat = Json.format[Meta]
  implicit val msisdnFormat = Json.format[Msisdn]

Output: List(Msisdn(Some(393823468684),Some(Meta(Some(10001771)))), Msisdn(Some(393823467689),None))

Then you can use

case class Msisdn(private val `primary-id`: Option[String],
                  private val meta: Option[Meta]) {
  def primaryId: Option[String] = `primary-id`
  def accountId: Option[String] = meta.flatMap(_.`related-account-id`)
}

to change public API.

2-nd way is use recursive path. But I think you can use it carefully.

  case class Msisdn(primaryId: Option[String], relatedAccountId: Option[String])
  object Msisdn {
    implicit val readData: Reads[Msisdn] = (
      (JsPath \ "primary-id").readNullable[String] ~
        (JsPath \\ "related-account-id").readNullable[String]
      ) (Msisdn.apply _)
  }

3-rd is use new Format. In this case you can work with json object, and check that field is exists.

There is another way, but I forgot how to do it. It's way used fmap, probably.

Sorry for my English.

edited Dec 10, 2019 at 21:37

answered Dec 7, 2019 at 10:04

Mikhail Ionkin

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6 Comments

cchantep Over a year ago

There is no need for the case class fields not to respect the usually naming just because it differ from the JSON one.

Avinash Reddy Over a year ago

@Mikhail Ionkin: The 2 way using recursive-path is not working. Even if the related-account-id value is present in the json, it is returning List(Msisdn(Some(393823468684),None), Msisdn(Some(393823467689),None))

Mikhail Ionkin Over a year ago

@AvinashReddy it's because grammar error in accoount in question. I copy it. Now i fix answer

Mikhail Ionkin Over a year ago

@cchantep which problems it's produce, if i will hide public API? I think that benefits of it covers disadvantages

cchantep Over a year ago

Don't think so, JSON is JSON, Scala is Scala

|

cchantep · Accepted Answer · 2019-12-07 14:27:19Z

There is no flatten annotation available, but playing by the rules make it easier.

import play.api.libs.json._

case class MsisdnMeta(relatedAccountId: Option[String])

object MsisdnMeta {
  private implicit val jsonConfiguration: JsonConfiguration =
    JsonConfiguration(JsonNaming { _ => "related-account-id" })

  implicit val format: OFormat[MsisdnMeta] = Json.format
}

case class Msisdn(
  primaryId: Option[String],
  meta: Option[MsisdnMeta]) {

  @inline def relatedAccountId: Option[String] =
    meta.flatMap(_.relatedAccountId)
}

object Msisdn {
  private implicit val jsonConfiguration: JsonConfiguration =
    JsonConfiguration(JsonNaming {
      case "primaryId" => "primary-id"
      case _ => "meta"
    })

  implicit val format: OFormat[Msisdn] = Json.format
}

Then reading/parsing JSON:

val json = Json.parse("""{
  "valid-for-start-datetime": "2019-08-23T10:47:17.485Z",
  "primary-id": "393823468684",
  "meta": {
    "related-account-id": "10001771",
    "roles": [
      "customer"
    ]
  }
}""")

val res = json.validate[Msisdn]
// play.api.libs.json.JsResult[Msisdn] = JsSuccess(Msisdn(Some(393823468684),Some(MsisdnMeta(Some(10001771)))),)

res.foreach { suc =>
  println(s"relatedAccountId = ${suc.relatedAccountId}")
}
// relatedAccountId = Some(10001771)

... and writing to JSON:

Json.toJson(Msisdn(Some("id"), Some(MsisdnMeta(Some("bar")))))
// play.api.libs.json.JsValue = {"primary-id":"id","meta":{"related-account-id":"bar"}}

The creation of Msisdn with the nested meta can be easier with some factory added to the companion object.

object Msisdn {
  // Added factory
  @inline def apply(
    primaryId: Option[String],
    relatedAccountId: String): Msisdn =
    Msisdn(primaryId, Some(MsisdnMeta(Some(relatedAccountId))))

  private implicit val jsonConfiguration: JsonConfiguration =
    JsonConfiguration(JsonNaming {
      case "primaryId" => "primary-id"
      case _ => "meta"
    })

  implicit val format: OFormat[Msisdn] = Json.format
}

Json.toJson(Msisdn(Some("id"), "bar"))
// play.api.libs.json.JsValue = {"primary-id":"id","meta":{"related-account-id":"bar"}}

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