Clarification of handling of Either + Conditional steps

[dspasojevic]

Hi,

I am looking at using traction to handle some of our SWF workload. I've been doing some testing to see what is possible, and have a couple of questions:

1. Does pickleSerializer support Either and Option? I don't seem to be able to get this to work. For example, in the console:

scala> import scala.pickling._, json._
import scala.pickling._
import json._

scala> import com.gravitydev.traction._
import com.gravitydev.traction._

scala> val s = pickleSerializer[Either[String, String]]
s: com.gravitydev.traction.PickleSerializer[Either[String,String]] = com.gravitydev.traction.PickleSerializer@b290aed

scala> s.serialize(Left("bob"))
scala.NotImplementedError: an implementation is missing
  at scala.Predef$.$qmark$qmark$qmark(Predef.scala:225)
  at scala.pickling.PicklerUnpicklerNotFound.pickle(Custom.scala:22)
  at com.gravitydev.traction.PickleSerializer.serialize(package.scala:7)
  ... 43 elided

I see the same failure if I change Sample to pass around Eithers (or Options).

1. Conditional Steps. I would like to be able to run different activities depending on the result of the previous activities. At the moment I am doing this by manually converting the Activity into a Step:

case class DoSomethingrecord: Record) extends Workflow[Record] {

  import model.Workflow._

  def flow: Step[Record] = {

    def complete(record: Record): Step[Record] = toStep1(UpdateRecord(record, "completed", None))(updateRecordA).map {
      _ match {
        case MFResult(_, Right(completedRecord)) => completedRecord
        case _ => Record("", "", "", None)
      }
    }

    def markFailed(record: Record): Step[Record] = toStep1(UpdateRecord(record, "failed", None))(updateRecordA).map {
      _ match {
        case MFResult(_, Right(failedRecord)) => failedRecord
        case _ => Record("", "", "", None)
      }
    }

    val starter: Step[Record] = toStep1(ProcessTheRecord(record))(processRecordA).flatMap( result => {
      result match {
        case MFResult(_, Right(processedRecord)) => complete(processedRecord)
        case MFResult(_, Left(error)) => {
          Console.out.println(s"Failed to update record: [$error]")
          markFailed(record)
        }
      }
    })

    starter
  }
}

This appears to do the correct thing, but I am wondering if there is there a nicer way of expressing that conditional workflow? I feel like I am missing something about how to support this. Do you think that I would be better off implementing a ConditionalStep as a peer to MappedStep, etc?

Thanks, -Dan

[alvaroc1]

Hi @dspasojevic A: 1. You are right, I hadn't tested Options and Eithers. At the moment, I think you would have to specify a separate instance for each serializer:

val leftS = pickleSerializer[Left[String, String]]
val rightS = pickleSerializer[Right[String, String]]

Not pretty, I know. I'll look into it and see if we can provide a better API for serializing those.

A: 2. I do think that Conditional steps should be peers to MappedStep. I was planning on building that, but haven't had time. I am not sure what the API should be yet. But the idea is that the entire workflow would always read nicely on a for-comprehension.

Let me know if that helps, I may get some time to work on these later in the week.

[alvaroc1]

@dspasojevic On the "upickle" branch, I switched to uPickle for the serialization. It seems to be much more capable and easier to work with. You might want to try that branch or here's the artifact:

"com.gravitydev" %% "traction-amazonswf" % "0.1.1-upickle-SNAPSHOT"

I'll merge that to master if things look good later in the week.

[dspasojevic]

Thanks @alvaroc1, for me at least, that change works great.

[dspasojevic]

Hi,

It looks like the more recent versions of upickle (I've tried 0.2.2 and 0.2.4) do not handle having a Iterable (or a case class that contains an Iterable) as a constructor argument to an activity. The same case class works as expected when used as a constructor argument to a workflow.

I've reverted to 0.1.7 and - with a bit of fooling around to get the implicits to the right spot - things work as I expected.

Thanks again.