Asynchronous wait for database-value in Playframework (2.4-M3) and Slick (3.0.0-RC3) - scala

Question

I'd like to keep my application as asynchronously as possible. Now I have this repository:
object LanguageRepository extends LanguageRepositoryTrait
{
private val languages = TableQuery[Languages]
private def db:Database = Database.forDataSource(DB.getDataSource())
private def filterQuery(id: Long): Query[Languages, Language, Seq] = languages.filter(_.id === id)
private def filterCode(code: String): Query[Languages, Language, Seq] = languages.filter(_.code === code)
private def all() : Query[Languages, Language, Seq] = languages
override def find(id: Long): Future[Language] =
{
try db.run(filterQuery(id).result.head)
finally db.close()
}
override def find(code: String): Future[Language] =
{
try db.run(filterCode(code).result.head)
finally db.close()
}
override def get(): Future[Seq[Language]] =
{
try db.run(all().result)
finally db.close()
}
}
When I call a url like "domain.tld/{language}" I want to check whether the given language(code) actually exists. Like, if the site isn't available in french (fr) I want to throw an exception or a 404.
Now, my problem is that this whole asynchronously thing is pretty cool and while I do think to understand the theory behind it, I'm rather baffled right now. I mean, I want this to be non-blocking (and asynchronously, which is the reason for me using Future and async ;))
In my controller I want to do something like:
def checkLanguage(language:String) = Action
{
val lang:Future[Language] = languageRepository.find(language)
lang.onComplete
{
case Success(s) = Ok("Yay")
case Failure(f) = 404("Oh no!")
}
}
Of course this can't work, but that's a schema of how I want to have things working. I want to wait or postpone the rendering of the site, until it's confirmed that the given language-code is valid or invalid.
I had a look at the Playframeworks async-documentation for 2.3.6 (https://www.playframework.com/documentation/2.3.6/ScalaAsync) but I couldn't really get this to work as intended.
Any input appreciated!

Answer 1

From your db query don't use .head instead use .headOption. that way ur return type will be a Future [Option [x]]
In ur controller u can do something like this
Lang.map { case Some (x) => Ok (x)
case None => 404 ( "not found ")
}

Answer 2

Try this,
Action.async {
val lang:Future[Option[Language]] = languageRepository.find(language)
lang.map {l => l.map{_ => Ok("Yay") }.getOrElse(NotFound("Oh no!"))
}
First of all, I am assuming that if there is a possibility that a language will not exist then languageRepository.find(language) should return an Option of Language. Change Future[Language] to Future[Result] and use Action.async instead of Action
Now for some explanation, Action takes a block whose result should be Result. However, what you get is Future[Option[Language]]. Play provides async method for Action which needs Future[Result] and it takes cares of completing the request.
So, you need to convert Future[Option[Language]] to Future[Result].
lang.map {l => l.map{_ => Ok("Yay") }.getOrElse(NotFound("Oh no!"))
We map over the lang, if the Option[Language] is not None then we convert it to Ok("yay") else we convert it to NotFound
Even, If you don't get Option[Language], the idea remains the same. Convert Future[Language] to Future[Result] and use Action.async instead of Action