# scala.collection.immutable.List out of VALUE_STRING when query with List[String] for multi-valued param
###### tags: `Scala`

- ReactiveMongo Version: 0.13.0

- MongoDB version 0.2.4(embedmongo)

- Operating System: MacOS 12.3 arm64 M1 chip

- JDK corretto-1.8 (java version: 1.8_362)

- Library Dependencies
Finatra/Finagle/Twitter Server

I have an API with a multi-valued parameter in single same key, just like: /api/designedservice?key1=value1&key1=value2

And I set a case class as the request parameter when query data by from DB, like:

case class GetValueFromDBReq(@QueryParam singleValue1: Option[String] = None, 
                             @QueryParam singleValue2: Option[String] = None,
                             @QueryParam multiValue: Option[List[String]] = None)

(the default value is set as for legacy design)

following is the DBqueryService I did:

class DBGetService @Inject()(@Coll coll: ScalaFuture[Maybe[BSONCollection]])
  extends Service[GetValueFromDBReq, Maybe[List[TargetCollection]]]{

 override def apply(req: GetValueFromDBReq): Future[Maybe[List[TargetCollection]] = {
     val con1 = BSONDocument("singleValue" => req.singleValue1)
     val con2 = BSONDocument("singleValue" => req.singleValue2)
     val con3 = req.multiValue match {
        case Some(s) => BSONDocument("multiValue" => BSONDocument("$in" -> s))
        case None     => BSONDocument()
     }

  ...

  coll.flatMap {

     case OK(c) => {

        (for {
            r <- c.find(con1 ++ con2 ++ con3)
                   .cursor[TargetCollection]()
                   .collect[List]
          } yield {
            r
          }).toTwitterFuture
             .map(a => OK(a))
             .handle {

             ....
            // error handling
             }

     }

  case KO(e) => {
     ...
    // error handling
     }

}
  }
}

The expected result is to return 200 with a List of the TargetCollection.
Currently it works when querying by singleValue1 and singleValue2 (or both), but when I used multiValue as the condition, it response 400 with following log:

[info]   Received Response:
[info]   HTTP/1.1 400 Bad Request
[info]   Date: Tue, 02 May 2023 03:15:12 GMT
[info]   Server: Finatra
[info]   Content-Length: 158
[info]   Content-Type: application/json; charset=utf-8
[info]   
[info]   {"errors":["multiValue: Cannot deserialize instance of `scala.collection.immutable.List` out of VALUE_STRING token\n at [Source: UNKNOWN; line: -1, column: -1]"]}

I've tried the following commands also:

val con3 = BSONDocument("multiValue" => req.multiValue)

val con3 = req.multiValue match {
  case Some(s) => s.map(r => BSONDocument("multiValue" -> r)).reduce(_ ++ _)
  case None => BSONDocument()
}

val con3 = req.multiValue match {
 case Some(s) => BSONDocument("multiValue" -> BSONDocument("$in" -> s.toArray))
 case None => BSONDocument()
}

val con3 = req.multiValue match {
 case Some(s) => BSONDocument("multiValue" -> BSONDocument("$in" -> BSONArray(s)))
 case None => BSONDocument()
}

val con3 = req.multiValue.map(x => BSONDocument("multiValue" -> BSONDocument("$in" -> x))) match{
    case Some(s) => s
    case None => BSONDocument()
}

And got the same error log.

Hope to know if there is anybody met the same problem before, thanks.