Using DynamoDB with Scala

Question

I'm working on this project in Scala and I'm testing one of my services with a local dynamodb database. I am using the 3rd party library awscala in order to access the table. I'm having a bit of trouble with this part of the code:

 override def put(status: Status) = {
   require(null != status, "The status object cannot be null.")

   table.put(status.id, "State" -> status.state)
 }

 override def get(id: String): Option[Status] = {
   require(StringUtils.isNotBlank(id), "The id of the status cannot be empty/null.")

   val state = dynamoDB.get(table, id)
   new Status(id, state)
 }

Status is a class that I define; it has fields ID: String and state: State, where State is a case class that I defined. When I get something from the table based on the id, and try to create a new Status object, the type of the thing returned is Option[awscala.dynamodbv2.Item] but it requires type enums.State (the case class I defined).

How would I case state to be of type enums.State?

EDIT: Added the definition of state and its case objects.

sealed trait State {}
case object COMPLETED_SUCCESSFULLY extends State {}
case object FINISHED_POLLING extends State {}
case object CURRENTLY_DOWNLOADING extends State {}
case object FINISHED_DOWNLOADING extends State {}

Can you show the definition of the enum State and its members? — mattinbits
– mattinbits, Commented Aug 14, 2015 at 8:50

mattinbits · Accepted Answer · 2015-08-14 13:32:00Z

2

Looking at the source code for the library you're using, it looks like table.put won't behave as you expect when the right hand side of -> is not a string, number, or byte buffer. It will store null.

https://github.com/seratch/AWScala/blob/master/src/main/scala/awscala/dynamodbv2/AttributeValue.scala

The relevant code is:

def toJavaValue(v: Any): aws.model.AttributeValue = {
    val value = new aws.model.AttributeValue
    v match {
      case null => null
      case s: String => value.withS(s)
      case n: java.lang.Number => value.withN(n.toString)
      case b: ByteBuffer => value.withB(b)
      case xs: Seq[_] => xs.headOption match {
        case Some(s: String) => value.withSS(xs.map(_.asInstanceOf[String]).asJava)
        case Some(n: java.lang.Number) => value.withSS(xs.map(_.toString).asJava)
        case Some(s: ByteBuffer) => value.withBS(xs.map(_.asInstanceOf[ByteBuffer]).asJava)
        case Some(v) => value.withSS(xs.map(_.toString).asJava)
        case _ => null
      }
      case _ => null
    }
  }

I suggest you write some code to marshall your enums to and from strings, and store and retrieve those.

answered Aug 14, 2015 at 13:32

mattinbits

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1 Comment

jstnchng Over a year ago

Yep that's what we ended up doing.

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