How to use $in mongo query with ReactiveMongo in Play! Framework 2.6?

Question

I am trying to use the following find query,

{
   "uid" : { "$in" : ["value1", "value2"] }
}

The array ["value1", "value2"] should be set dynamically from Scala Array[String].

Here is my code,

    def find(uids: Array[String]): Future[Seq[User]] = {
    val query: JsObject = Json.parse(JsonUtil.toInQuery(uids, "uid")).asInstanceOf[JsObject]
    collection.flatMap(_.find(query)
      .cursor[User](ReadPreference.primary)
      .collect[Seq]()
    )
  }

The method JsonUtil.toInQuery(uids, "uid") is creating the json string of the query. I have tried using BSONDocument and writing Json query manually instead of passing json string, but it does not seem to work.

Can anyone suggest me a working way to use that query in reactive-mongo with play framework 2.6 ?

Update

public static String toJsonString(String[] arr){
        return Json.toJson(arr).toString();
    }

public static String toInQuery(String[] arr, String item){
    return "{ \""+item+"\": {\"$in\": "+toJsonString(arr)+"}}";
}

I got it working. But, not sure if this is the correct approach.