Retrieving a particular field inside objects in JsArray

Question

A part of my JSON response looks like this:

"resources": [{
        "password": "",
        "metadata": {
            "updated_at": "20190806172149Z",
            "guid": "e1be511a-eb8e-1038-9547-0fff94eeae4b",
            "created_at": "20190405013547Z",
            "url": ""
        },
        "iam": false,
        "email": "<some mail id>",
        "authentication": {
            "method": "internal",
            "policy_id": "Default"
        }
    }, {
        "password": "",
        "metadata": {
            "updated_at": "20190416192020Z",
            "guid": "6b47118c-f4c8-1038-8d93-ed6d7155964a",
            "created_at": "20190416192020Z",
            "url": ""
        },
        "iam": true,
        "email": "<some mail id>",
        "authentication": {
            "method": "internal",
            "policy_id": null
        }
    },
    ...
]

I am using Json helpers provided by the Play framework to parse this Json like this:

val resources: JsArray = response("resources").as[JsArray]

Now I need to extract the field email from all these objects in the resources JsArray. For this I tried writing a foreach loop like:

for (resource <- resources) {

}

But I'm getting an error Cannot resolve symbol foreach at the <- sign. How do I retrieve a particular field like email from each of the JSON objects inside a JsArray

pme · Accepted Answer · 2019-08-09 14:24:51Z

2

With Play JSON I always use case classes. So your example would look like:

import play.api.libs.json._

case class Resource(password: String, metadata: JsObject, iam: Boolean, email: String, authentication: JsObject)

object Resource {
  implicit val jsonFormat: Format[Resource] = Json.format[Resource]
}

val resources: Seq[Resource] = response("resources").validate[Seq[Resource]] match {
  case JsSuccess(res, _) => res
  case errors => // handle errors , e.g. throw new IllegalArgumentException(..)
}

Now you can access any field in a type-safe manner.

Of course you can replace the JsObjects with case classes in the same way - let me know if you need this in my answer.

But in your case as you only need the email there is no need:

resources.map(_.email) // returns Seq[String]

edited Aug 9, 2019 at 14:24

answered Aug 8, 2019 at 7:33

pme

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4 Comments

pme Over a year ago

@Pedro Correia Luís thanks for the hint - I adjusted my answer

Sparker0i Over a year ago

Hey, thanks for the answer. Right now my requirement is only getting Email, but this is not the entire output, and just like metadata and authorization, I have some other stuff as well which will be needed to extract. Could you please edit the answer to show with case classes?

Sparker0i Over a year ago

I'm not sure how I handle the errors. I know that if there is a problem parsing any field, it will be an error, but how do I handle because the output of the case errors also expects an object of type Resource

pme Over a year ago

@Sparker0i 1. Pedro's answer did already provide that in his answer. 2. a more functional way would be to return Try[Seq[Resource]] and handle the error case at a later point.

Pedro Correia Luis · Accepted Answer · 2019-08-08 09:07:36Z

0

So like @pme said you should work with case classes, they should look something like this:

import java.util.UUID

import play.api.libs.json._


case class Resource(password:String, metadata: Metadata, iam:Boolean, email:UUID, authentication:Authentication)

object Resource{
  implicit val resourcesImplicit: OFormat[Resource] = Json.format[Resource]
}

case class Metadata(updatedAt:String, guid:UUID, createdAt:String, url:String)

object Metadata{
  implicit val metadataImplicit: OFormat[Metadata] = Json.format[Metadata]
}


case class Authentication(method:String, policyId: String)

object Authentication{
  implicit val authenticationImplicit: OFormat[Authentication] = 
Json.format[Authentication]
}

You can also use Writes and Reads instead of OFormat, or custom Writes and Reads, I used OFormat because it is less verbose.

Then when you have your responses, you validate them, you can validate them the way @pme said, or the way I do it:

val response_ = response("resources").validate[Seq[Resource]]
response_.fold(
    errors => Future.succeful(BadRequest(JsError.toJson(errors)),
resources => resources.map(_.email))// extracting emails from your objects
    ???
)

So here you do something when the Json is invalid, and another thing when Json is valid, the behavior is the same as what pme did, just a bit more elegant in my opinion

answered Aug 8, 2019 at 9:07

Pedro Correia Luis

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5 Comments

cchantep Over a year ago

If the goal is to get a single value email: String (to ends with a Seq[String]) per array element, there is no need to add a case class ("just" to benefit from the macro generated Reads)

cchantep Over a year ago

And so? A email is not a structures type (a Value class rather than a Case class)

Sparker0i Over a year ago

@pedro, I tried your code of the response part, but I am getting error at the BadRequest part.

Sparker0i Over a year ago

Here. I'm using the latest Play framework. Maybe that's why..?

Pedro Correia Luis Over a year ago

I don´t think that's the case, probably an import missing. If you take BadRequest you still have the error? also take the ???, was just because I didn't know what else you wanted to do after having the emails

oneDerer · Accepted Answer · 2019-08-09 09:44:20Z

Assuming that your json looks like this:

val jsonString =
  """
    |{
    |  "resources": [
    |    {
    |      "password": "",
    |      "metadata": {
    |        "updated_at": "20190806172149Z",
    |        "guid": "e1be511a-eb8e-1038-9547-0fff94eeae4b",
    |        "created_at": "20190405013547Z",
    |        "url": ""
    |      },
    |      "iam": false,
    |      "email": "<some mail id1>",
    |      "authentication": {
    |        "method": "internal",
    |        "policy_id": "Default"
    |      }
    |    },
    |    {
    |      "password": "",
    |      "metadata": {
    |        "updated_at": "20190416192020Z",
    |        "guid": "6b47118c-f4c8-1038-8d93-ed6d7155964a",
    |        "created_at": "20190416192020Z",
    |        "url": ""
    |      },
    |      "iam": true,
    |      "email": "<some mail id2>",
    |      "authentication": {
    |        "method": "internal",
    |        "policy_id": null
    |      }
    |    }
    |  ]
    |}
  """.stripMargin

you can do:

(Json.parse(jsonString) \ "resources").as[JsValue] match{
  case js: JsArray => js.value.foreach(x => println((x \ "email").as[String]))
  case x => println((x \ "email").as[String])
}

or:

(Json.parse(jsonString) \ "resources").validate[JsArray] match {
  case s: JsSuccess[JsArray] => s.get.value.foreach(x => println((x \ "email").as[String]))
  case _: JsError => arr().value //or do something else
}

both works for me.

cchantep · Accepted Answer · 2019-08-08 08:04:42Z

-1

The resources is a JsArray, a type that doesn't provide .flatMap so cannot be used at right of <- in a for comprehension.

val emailReads: Reads[String] = (JsPath \ "email").reads[String]
val resourcesReads = Reads.seqReads(emailReads)

val r: JsResult[Seq[String]] = resources.validate(resources reads)

answered Aug 8, 2019 at 8:04

cchantep

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1 Comment

cchantep Over a year ago

That's not what I want

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