PlayFramework2中的toJson用于对象列表

Question

I've read this answer about how simple it is..

But if if I have list of Objects but not just strings:

case class Article(
     title:String,
     description:String,
     examples: List[Example]
)

There is Example case class:

case class Example(meaning:String, proofs:List[String])

Then how I could transform my Article to json string?

If I use:

  def article(word:String) = Action {

    implicit val articleFormat = Json.format[Article]
    implicit val exampleFormat = Json.format[Example]

    val article = Article.article(word)

    Ok( Json.format(article) )

    // or: ?

    Ok( Json.obj("examples" -> article.examples) ) // this works but only for Examples alone.. without Article

    // or: ? 
     Ok( Json.obj("article" -> article) )

   // or:?

    Ok(
     Json.toJson( // works, but it is still not that I'm expecting (duplication of "examples"...like: "examples":"{\"examples\":[{\"meaning\":\"meaning1\",...)
       Map(
         "title" -> article.title,
         "description" -> article.description,
         "examples" -> Json.obj("examples" -> article.examples).toString()
       )
     )
   )

  }

I got an error: No unapply function found

When I try to write my unapply method, I got different error about apply.. Don't want to spoil.. Do you have an answer or at least a suggestion?

Answer 1

Along with your model, you can define an implicit typeclass Writes[T] which is able to convert your model into a JsValue :

implicit object ExampleWrites extends Writes[Example] {
  def writes(e: Example) = Json.obj(
    "meaning" -> e.meaning,
    "proofs" -> e.proofs
  )
}
implicit object ArticleWrites extends Writes[Article] {
  def writes(a: Article) = Json.obj(
    "title" -> a.title,
    "description" -> a.description,
    "examples" -> a.examples
  )
}

Then it is as simple as: Json.toJson(article)