CODEWITHSUNDEEP
reactive-programmingrx-scala
Julio Faerman
Julio Faerman

Reputation: 13501

How to observe on reverse dependency order?

I'd like to observe a tree of objects, in reverse dependency order, but do not know what combinators to use. The specific case is iterating through AWS Resources in order for deletion, for example deleting S3 Objects before deleting their S3 Buckets, like this:

  val S3 = new AmazonS3Client

  val buckets = Observable.from {
    S3.listBuckets.asScala
  }

  val objects = buckets.flatMap { b => Observable.from(
    S3.listObjects(new ListObjectsRequest().withBucketName(b.getName))
      .getObjectSummaries
      .asScala)
  }

  val combined:Observable[_] = ???

  for (thing <- combined) thing match {
    case b:Bucket => println("delete bucket")
    case o:S3ObjectSummary => println("delete object")
  }

So, the final combined observable should emit all the objects before emitting the bucket. What combinator should i use for that?

Upvotes: 0

Views: 108

Answers (1)

zsxwing
zsxwing

Reputation: 20816

You can append b to the end of its objects, e.g.,

val objects = buckets.flatMap { b => Observable.from(
  S3.listObjects(new ListObjectsRequest().withBucketName(b.getName))
    .getObjectSummaries
    .asScala) :+ b
}

Upvotes: 1

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