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`.
For others who came here looking for a slight variant where we override `reads` and `writes` in the Format class (like the [example given](https://www.playframework.com/documentation/2.0/api/scala/play/api/libs/json/package.html) on the API docs), you can declare a lazy reference to your needed object:

```
  lazy val tweetFormat: Format[Tweet] = TweetFormat
  implicit object UserFormat extends Format[User] {
  //...
  }

  //...
  implicit object TweetFormat extends Format[Tweet] {
  //...

```