Scala: Chaining futures, returning the first

Question

I have a scenario where I have a Future[Something] : a which when successful needs to trigger a second Future[Unit] : b . I want to chain a and b together but I only care that a succeeds. if b fails I can just log an error and leave it at that:

So far I have:

def updateSomething(something: Something): Future[Something] = {
    val eventual: Future[Something] = repository.update(something)
    eventual.onSuccess({
      case updated =>
        repository.audit(updated.id, "Update successful")
          .onFailure({
            case throwable: Throwable => Logger.error("Audit failed", throwable)
          })
        Logger.info("Update Complete")
    })
    eventual
}

But this does not link the lifecyles of the update and the audit together. eg when I Await.result(service.updateSomething(...), duration) there is no guarantee the repository.audit future has completed.

Answer 1

flatMap is your friend. You can just use a for-comprehension + recover:

for {
  a <- executeA()
  _ <- executeB(b).recover{case e => println(e); Future.unit } // awaits B to complete
} yield a

Answer 2

Also you can use more friendly form:

execudeA().flatMap(a =>
  executeB().recover { case e => println(e); () }.map(_ => a)
)

Answer 3

also, you can just use a val

val = a <- executeA()
a.andThen{ case _ => executeB(b).recover{case e => println(e)} }
a //and return a