How to solve Scala asynchronous behaviour - scala

Question

In my backend controller function I have the following code:
def getContentComponents = Action.async {
contentComponentDTO.list().map { contentComponentsFuture =>
contentComponentsFuture.foreach(contentComponentFuture =>
contentComponentFuture.typeOf match {
case 5 => contentComponentDTO.getContentComponentText(contentComponentFuture.id.get).map(text => {
contentComponentFuture.text = text.text
println(contentComponentFuture.text)
})
}
)
Ok(Json.toJson(contentComponentsFuture))
}
}
The problem is, that OK() is called before the stuff above is finished. Is there a smart way to wait until the foreach is finished?
thanks
That have been two differen questions with different problems! So thats the reason for two questions looking similar

Answer 1

There are two approaches that you can take, but before going to that let's recap what you are trying to do.
You have a list of items contentComponentsFuture, I am assuming retrieving from database, which is why you are getting a future.
Now your contentComponentsFuture is a mutable variable (which I strongly suggest not to use, stick to immutable data) has a text field which you need to update.
Now all that code block before the Ok() will return a future as it is working on a future list. So the easiest solution is to do a map over the future and return the result. The map over a future is just a onComplete function which triggers once the future is resolved. So the code will look like:
def getContentComponents = Action.async {
val futureResult = contentComponentDTO.list().map { contentComponentsFuture =>
contentComponentsFuture.map(contentComponentFuture =>
contentComponentFuture.typeOf match {
case 5 => contentComponentDTO.getContentComponentText(contentComponentFuture.id.get).map(text => {
contentComponentFuture.text = text.text
contentComponentFuture
})
}
)
}
futureResult.map(result => {
Future.sequence(result).map(t => Ok(Json.toJson(t))
}))
}
The other option will be to use scala asycn library: https://github.com/scala/scala-async
which gives a handy wrapper so that you do not need to map over future explicitly, the same code above with scala async library will look like below:
def getContentComponents = Action.async {
Async.async {
val result = Async.await(contentComponentDTO.list().map { contentComponentsFuture =>
contentComponentsFuture.map(contentComponentFuture =>
contentComponentFuture.typeOf match {
case 5 => contentComponentDTO.getContentComponentText(contentComponentFuture.id.get).map(text => {
contentComponentFuture.text = text.text
contentComponentFuture
})
}
)
})
Ok(Json.toJson(result))
}
}