How do you create Json object with values of different types?

Question

How do you create Json object with values of different types ?

I'm using spray-json

Here is the code

val images : List[JsObject] = fetchImageUrls(url).map((url: String) => {
  JsObject(List(
        "link_path" -> JsString(url),
        "display_name" -> JsString("image"),
        "size" -> JsString(""),
        "modified" -> JsString(""),
        "thumbnail" -> JsString(url),
        "filename" -> JsString("image"),
        "is_dir" -> JsBoolean(x = false),
        "thumb_exists" -> JsBoolean(x = true)) )
  })

val jsonAst: JsObject = JsObject(List(
  "client" -> JsString("urlimages"),
  "view" -> JsString("thumbnails"),
  "contents" -> JsArray(images)
))

It works but looks really heavy. Is there a way to define json with code like this ?

val images : List[List[(String, Any)]] = fetchImageUrls(url).map((url: String) => {
  List(
    "link_path" -> url,
    "display_name" -> "image",
    "size" -> "",
    "modified" -> "",
    "thumbnail" -> url,
    "filename" -> "image",
    "is_dir" -> false,
    "thumb_exists" -> true)
})

val jsonAst = List(
  "client" -> "urlimages",
  "view" -> "thumbnails",
  "contents" -> images
).toJson

It doesn't work saying that

Cannot find JsonWriter or JsonFormat type class for List[(String, Object)]
    ).toJson
      ^

Which I get, type of each field is not defined at compile time. But why wouldn't it work if serializer does pattern matching anyway ?

Thanks!

Answer 1

You are going for the wrong approach here. For consistency purposes I would strongly encourage you to use a case class.

Say you have this

case class Image(
    url: String,
    size: Double,
    properties: Map[String][String]
    optionalProperty: Option[String]
    // etc.
);

And then you use parse and decompose to deal with this.

val image = parse(jsonString).extract[Image]; // extracts an Image from JSON.
val jsonForImage: JValue = decompose(image);  // serializes an Image to JSON.

And if you want to serialize a List[Image] to JSON:

def serialize(images: List[Image]) : JValue = {
    for (image <- images) 
       yield decompose(image);
};

To parse a list of images from JSON:

val images: List[Image] = parse(jsonString).extract[List[Image]];

Using Option[SomeType] in the Image case class will deal with missing/optional parameters automatically.