scala, play, futures: combining results from multiple futures - scala

Question

I am using:
Scala 2.10
Play 2.1
Currently, I am using the Future class from scala.concurrent._, but I'm open to trying another API.
I am having trouble combining the results of multiple futures into a single List[(String, String)].
The following Controller method successfully returns the results of a single Future to an HTML template:
def test = Action { implicit request =>
queryForm.bindFromRequest.fold(
formWithErrors => Ok("Error!"),
query => {
Async {
getSearchResponse(query, 0).map { response =>
Ok(views.html.form(queryForm,
getAuthors(response.body, List[(String, String)]())))
}
}
})
}
The method getSearchResult(String, Int) performs a web service API call and returns a Future[play.api.libs.ws.Response]. The method getAuthors(String, List[(String, String)]) returns a List[(String, String)] to the HTML template.
Now, I am trying to call getSearchResult(String, Int) in a for loop to get several Response bodies. The following should give an idea of what I'm trying to do, but I get a compile-time error:
def test = Action { implicit request =>
queryForm.bindFromRequest.fold(
formWithErrors => Ok("Error!"),
query => {
Async {
val authors = for (i <- 0 to 100; if i % 10 == 0) yield {
getSearchResponse(query, i)
}.map { response =>
getAuthors(response.body, List[(String, String)]())
}
Ok(views.html.form(queryForm, authors))
}
})
}
type mismatch; found : scala.collection.immutable.IndexedSeq[scala.concurrent.Future[List[(String, String)]]] required: List[(String, String)]
How can I map the responses of several Future objects to a single Result?

Answer 1

Create a Future parametrized by a List or other Collection of the Result type.
From here:
In Play 1 you can do this:
F.Promise<List<WS.HttpResponse>> promises = F.Promise.waitAll(remoteCall1, remoteCall2, remoteCall3);
// where remoteCall1..3 are promises
List<WS.HttpResponse> httpResponses = await(promises); // request gets suspended here
In Play 2 less direct:
val httpResponses = for {
result1 <- remoteCall1
result2 <- remoteCall2
} yield List(result1, result2)