[spray-json] Optional field in case class

[Marcin Szekalski]

Hey,

I'm using Salat library for serializing case classes as mongoDb objects. My Item.scala file looks like this:

case class Item(_id: String = (new ObjectId).toString, itemId: Int, var name: String, var active: Boolean) extends WithId {

  override def id: ObjectId = new ObjectId(_id)

}

object Item extends MongoDb[Item] with MongoDao[Item] {

  override def collectionName: String = "items"

}

object ItemJsonProtocol extends DefaultJsonProtocol {

  implicit val itemFormat = jsonFormat4(Item.apply)

}

Now, I'm using it to post the Item entities as Json via Spray HTTP. I'd want to invoke it as follows: curl.exe -H "Content-Type: application/json" -X PUT -d "{\"itemId\": 1, \"active\":true}" http://localhost:8080/items/ hoping it would provide generated id if I don't provide one.

However, after invoking curl command I'm getting an error:

The request content was malformed:

Object is missing required member '_id'

Is there any way to mark the _id field as optional without making the Option out of it (this field will always be set) and defining custom JsonFormat thus (de)serializing the object by myself?

Best,

Marcin

[Marcin Szekalski]

Ooops... Sorry, I posted the wrong curl command. The correct is (I'm invoking it on Window's cmd.exe):

curl.exe -H "Content-Type: application/json" -X PUT -d "{\"itemId\": 1, \"active\":true, \"name\" : \"test\"}" http://localhost:8080/items/

[Mathias Doenitz]

Marcin,

if you write a custom JsonFormat this is no problem.
If you wanted to stick with the `jsonFormat` helper you’d have to move the `_id` member out of the constructor:

case class Item(itemId: Int, var name: String, var active: Boolean) extends WithId {
val _id: String = (new ObjectId).toString
}

Cheers,
Mathias

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[Marcin Szekalski]

Hey,

What I'd want to achieve is:

Accept both:

• {"itemId": 1, "active":true}
  
• {"_id": "123456712345671234567890", "itemId": 1, "active":true}

while reading, and ALWAYS writing _id when serializing to JSON.

Is there any other way than writing custom JsonFormat?

Sorry, for newbie's questions, I'm really new.

Best,

Marcin

[Mathias Doenitz]

Marcin,

what you are looking for required custom logic being run during deserialisation.
Therefore the standard `jsonFormat` helper will not be able to solve things for you here.
You’ll have to resort to writing a custom `JsonFormat` as described here:
https://github.com/spray/spray-json#providing-jsonformats-for-other-types

Cheers,
Mathias

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[Marcin Szekalski]

Hey,

I did write those formats and it works now. One of them looks like this:

  implicit object ItemJsonFormat extends RootJsonFormat[Item] {
    override def read(json: JsValue): Item = json.asJsObject.getFields("_id", "itemId", "name", "active") match {
      case Seq(JsString(_id), JsNumber(itemId), JsString(name), JsBoolean(active)) => Item(_id = _id, itemId = itemId.toInt, name = name, active = active)
      case Seq(JsNumber(itemId), JsString(name), JsBoolean(active)) => Item(itemId = itemId.toInt, name = name, active = active)
      case _ => throw new DeserializationException("Item expected")
    }
    override def write(obj: Item): JsValue = JsObject(
      "_id" -> JsString(obj._id),
      "itemId" -> JsNumber(obj.itemId),
      "name" -> JsString(obj.name),
      "active" -> JsBoolean(obj.active)
    )
  }

One other thing which might cause some trouble but in my opinion deserves mentioning somewhere - if anyone has a problem with nested objects ("non-primitive" types) - I advise using .toJson in write def (like obj.time.toJson, where obj.time is jodatime's DateTime) and JsValue's .convertTo[T] def in read, like time = JsString(time).convertTo[DateTime]. In order for this to work there have to be defined implicit json formats for those "non-primitive" objects.

Best,

Marcin

[Kunal Parikh]

Marcin,

I am having the same problem. I am trying to read curl HTTP POST message & parse /unmarshal json object.

Could you please share your complete code ?

I am not sure how unmarshalling works, I tried various way but i am not able to unmarshal JSON object.

Thanks

Kunal

[Mathias Doenitz]

> I am trying to read curl HTTP POST message & parse /unmarshal json object.

What exactly are you trying to do?
What code do you already have and in what way doesn’t it do what you think it does?

Cheers,
Mathias

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[Qoo Mak]

Marcin

Or you could be just a little less orthodox and use json4s and enjoy having case class Item(_id: Option[String], itemId: Int, name: String, active: Boolean)

And never write customJsonFormat again

Sorry

--

qoomak