Modify Future[JsArray] in Scala - mongodb

Question

I use the Play 2.0 framework for getting data from my MongoDB.
This is done by the following code:
def getTopicsInAppFormat = Action.async {
// let's do our query
val cursor: Cursor[TopicModel] = topicCollection.find(Json.obj()).cursor[TopicModel]
// gather all the JsObjects in a list
val futureTopicsList: Future[List[TopicModel]] = cursor.collect[List]()
// transform the list into a JsArray
val futurePersonsJsonArray: Future[JsArray] = futureTopicsList.map { topics =>
Json.arr(topics)
}
// everything's ok! Let's reply with the array
futurePersonsJsonArray.map {
topics =>
Ok(topics(0))
}
}
But the problem is that I want the function to return an alternative representation of the data. So, I want for example to change the amount of attributes, etc. What is a good way to achieve that? I tried to modify the data (respectively create a new array with the new format) in the last step, right before the Ok() function. However, I didn't have any progress with that :/
EDIT:
At the moment I'm trying to create new JSON objects but I'm stuck while getting the data from the original one...
My current code looks like this:
futurePersonsJsonArray.map {
topics =>
/* Access a attribute */
println(topics(0).\("content"))
/* However: error: JsUndefined('content' is undefined on object */
/* Could be used to set the new attributes */
val myNewJson = Json.obj(
"name" -> "JohnDoe",
"age" -> "123",
"created" -> new java.util.Date().getTime())
Ok(/*topics(0)*/myNewJson)
}

Answer 1

You're probably misinterpreting the format of topics. The message you're getting is telling you that there is no content property on the first element of the topics array. This is a simplified example:
val myObject = Json.obj("a" -> 1, "b" -> 2)
myObject \ "a" //JsNumber(1)
myObject \ "c" //JsUndefined('c' is undefined on object...)
This makes sense, since we get undefined in Javascript when trying to read a property that doesn't exist. In the Play Json library, \ always returns a JsValue, and one of its subtypes is JsUndefined.
You should reexamine the format of the objects in the topics array and reassess how you can access its values.

Answer 2

Now, my final solution for the problem "modify the data just before returning" looks like this:
futurePersonsJsonArray.map {
topics =>
def createNewFormat(uID: JsValue, name: JsValue, content: JsValue, lat: JsValue, lng: JsValue): JsObject = {
return Json.obj(
"id" -> uID,
[...]
}
/* Access the needed attributes */
val uIDs = topics(0).\\("uID")
val names = topics(0).\\("name")
val content = topics(0).\\("content")
val gps = topics(0).\\("gps")
var dataArray = new JsArray()
/* create new Array */
for( i <- 0 to uIDs.length-1){
dataArray = dataArray.append(createNewFormat(uIDs(i),names(i),content(i),gps(i)(0),gps(i)(1)))
}
/* put this into a new JSObject */
var returnThis = Json.obj("data" -> dataArray)
Ok(returnThis)
}
Maybe this does help someone with similar problems :)