<p>I have defined a couple of case classes for JSON representation but I am not sure whether I did it properly as there a lot of nested case classes.
Entities like spec, meta and so on are of type JSONObject as well as the Custom object itself.</p>

<p>Here is all the classes I have defined:</p>

<pre><code>  case class CustomObject(apiVersion: String,kind: String, metadata: Metadata,spec: Spec,labels: Object,version: String)

  case class Metadata(creationTimestamp: String, generation: Int, uid: String,resourceVersion: String,name: String,namespace: String,selfLink: String)

  case class Spec(mode: String,image: String,imagePullPolicy: String, mainApplicationFile: String,mainClass: String,deps: Deps,driver: Driver,executor: Executor,subresources: Subresources)

  case class Driver(cores: Double,coreLimit: String,memory: String,serviceAccount: String,labels: Labels)

  case class Executor(cores: Double,instances: Double,memory: String,labels: Labels)

  case class Labels(version: String)

  case class Subresources(status: Status)

  case class Status()

  case class Deps()
</code></pre>

<p>And this is a JSON structure for the custom K8s object I need to transform:</p>

<pre><code>{
    "apiVersion": "sparkoperator.k8s.io/v1alpha1",
    "kind": "SparkApplication",
    "metadata": {
        "creationTimestamp": "2019-01-11T15:58:45Z",
        "generation": 1,
        "name": "spark-example",
        "namespace": "default",
        "resourceVersion": "268972",
        "selfLink": "/apis/sparkoperator.k8s.io/v1alpha1/namespaces/default/sparkapplications/spark-example",
        "uid": "uid"
    },
    "spec": {
        "deps": {},
        "driver": {
            "coreLimit": "1000m",
            "cores": 0.1,
            "labels": {
                "version": "2.4.0"
            },
            "memory": "1024m",
            "serviceAccount": "default"
        },
        "executor": {
            "cores": 1,
            "instances": 1,
            "labels": {
                "version": "2.4.0"
            },
            "memory": "1024m"
        },
        "image": "gcr.io/ynli-k8s/spark:v2.4.0,
        "imagePullPolicy": "Always",
        "mainApplicationFile": "http://localhost:8089/spark_k8s_airflow.jar",
        "mainClass": "org.apache.spark.examples.SparkExample",
        "mode": "cluster",
        "subresources": {
            "status": {}
        },
        "type": "Scala"
    }
}
</code></pre>

<p>UPDATE:
I want to convert JSON into case classes with Circe, however, with such classes I face this error:</p>

<pre><code>Error: could not find Lazy implicit value of type io.circe.generic.decoding.DerivedDecoder[dataModel.CustomObject]
    implicit val customObjectDecoder: Decoder[CustomObject] = deriveDecoder[CustomObject]
</code></pre>

<p>I have defined implicit decoders for all case classes:</p>

<pre><code> implicit val customObjectLabelsDecoder: Decoder[Labels] = deriveDecoder[Labels]
    implicit val customObjectSubresourcesDecoder: Decoder[Subresources] = deriveDecoder[Subresources]
    implicit val customObjectDepsDecoder: Decoder[Deps] = deriveDecoder[Deps]
    implicit val customObjectStatusDecoder: Decoder[Status] = deriveDecoder[Status]
    implicit val customObjectExecutorDecoder: Decoder[Executor] = deriveDecoder[Executor]
    implicit val customObjectDriverDecoder: Decoder[Driver] = deriveDecoder[Driver]
    implicit val customObjectSpecDecoder: Decoder[Spec] = deriveDecoder[Spec]
    implicit val customObjectMetadataDecoder: Decoder[Metadata] = deriveDecoder[Metadata]
    implicit val customObjectDecoder: Decoder[CustomObject] = deriveDecoder[CustomObject]
</code></pre>

<p>The reason you can't derive a decode for <code>CustomObject</code> is because of the <code>labels: Object</code> member. </p>

<p>In circe all decoding is driven by static types, and circe does not provide encoders or decoders for types like <code>Object</code> or <code>Any</code>, which have no useful static information. </p>

<p>If you change that case class to something like the following:</p>

<pre><code>case class CustomObject(apiVersion: String, kind: String, metadata: Metadata, spec: Spec)
</code></pre>

<p>…and leave the rest of your code as is, with the import:</p>

<pre><code>import io.circe.Decoder, io.circe.generic.semiauto.deriveDecoder
</code></pre>

<p>And define your JSON document as <code>doc</code> (after adding a quotation mark to the <code>"image": "gcr.io/ynli-k8s/spark:v2.4.0,</code> line to make it valid JSON), the following should work just fine:</p>

<pre><code>scala&gt; io.circe.jawn.decode[CustomObject](doc)
res0: Either[io.circe.Error,CustomObject] = Right(CustomObject(sparkoperator.k8s.io/v1alpha1,SparkApplication,Metadata(2019-01-11T15:58:45Z,1,uid,268972,spark-example,default,/apis/sparkoperator.k8s.io/v1alpha1/namespaces/default/sparkapplications/spark-example),Spec(cluster,gcr.io/ynli-k8s/spark:v2.4.0,Always,http://localhost:8089/spark_k8s_airflow.jar,org.apache.spark.examples.SparkExample,Deps(),Driver(0.1,1000m,1024m,default,Labels(2.4.0)),Executor(1.0,1.0,1024m,Labels(2.4.0)),Subresources(Status()))))
</code></pre>

<p>Despite what one of the other answers says, circe can definitely derive encoders and decoders for case classes with no members—that's definitely not the problem here.</p>

<p>As a side note, I wish it were possible to have better error messages than this:</p>

<pre><code>Error: could not find Lazy implicit value of type io.circe.generic.decoding.DerivedDecoder[dataModel.CustomObject
</code></pre>

<p>But given the way circe-generic has to use Shapeless's <code>Lazy</code> right now, this is the best we can get. You can try <a href="https://github.com/circe/circe-derivation" rel="nofollow noreferrer">circe-derivation</a> for a mostly drop-in alternative for circe-generic's semi-automatic derivation that has better error messages (and some other advantages), or you can use a compiler plugin like <a href="https://github.com/tek/splain" rel="nofollow noreferrer">splain</a> that's specifically designed to give better error messages even in the presence of things like <code>shapeless.Lazy</code>.</p>

<p>As one final note, you can clean up your semi-automatic definitions a bit by letting the type parameter on <code>deriveDecoder</code> be inferred:</p>

<pre><code>implicit val customObjectLabelsDecoder: Decoder[Labels] = deriveDecoder
</code></pre>

<p>This is entirely a matter of taste, but I find it a little less noisy to read.</p>
