Question: I have a recursive class defined :

```
case class SettingsRepository(id: Option[BSONObjectID],
                          name: Option[String],
                          children: Option[List[SettingsRepository]])

```

with a JSON implicit format as below :

```
implicit val repositoryFormat = Json.format[SettingsRepository]

```

How can I do to resolve this compilation error? :

```
No implicit format for Option[List[models.practice.SettingsRepository]] available.
In /path/to/the/file.scala:95

95 implicit val repositoryFormat = Json.format[SettingsRepository] 

```

I tried to define a lazy reads/write/format wrapper without any success...
Anyone know a clean way to do that?

Answer: 
As you've discovered, you can't use the JSON inception macro here, but you can write your own `Format` (note that I've replaced `BSONObjectID` with `Long` for the sake of a complete working example):

```
import play.api.libs.functional.syntax._
import play.api.libs.json._

case class SettingsRepository(
  id: Option[Long],
  name: Option[String],
  children: Option[List[SettingsRepository]]
)

implicit val repositoryFormat: Format[SettingsRepository] = (
  (__ \ 'id).formatNullable[Long] and
  (__ \ 'name).formatNullable[String] and
  (__ \ 'children).lazyFormatNullable(implicitly[Format[List[SettingsRepository]]])
)(SettingsRepository.apply, unlift(SettingsRepository.unapply))

```

The trick is providing an explicit type annotation and using `implicitly` rather than just a type parameter on `lazyFormatNullable`.
Just an update. This is already fixed for a long time. For example, in `play-json` version 2.3.9, which is the oldest available at [Maven](https://mvnrepository.com/artifact/com.typesafe.play/play-json), the following works:

```
import play.api.libs.json._

case class SettingsRepository(id: Option[Int],
                              name: Option[String],
                              children: Option[List[SettingsRepository]])

implicit val repositoryFormat = Json.format[SettingsRepository]

val s = SettingsRepository(Some(2), Some("name"), Some(List(SettingsRepository(Some(1), Some(""), None))))
println(Json.toJsObject(s))

```

and outputs:

```
{"id":2,"name":"name","children":[{"id":1,"name":""}]}

```

Code run at [Scastie](https://scastie.scala-lang.org/toshetah/GyaQDCyyTUuJVNeaaqmB8w/9).