I use the Enumerator pattern to retrieve some tweets every second with WS.url
Enumerator.fromCallback[String](() =>
Promise.timeout(WS.url("http://search.twitter.com/search.json?q="+query+"&rpp=1").get().map { response =>
val tweets = response.json \\ "text"
tweets match {
case Nil => "Nothing found!"
case head :: tail => query + " : " + head.as[String]
}
}.map(Some.apply).value.get, 1000 milliseconds)
)
My is problem is that
Enumerator.fromCallback[String]()
is waiting for a
Promise[Option[String]]
As WS.url(...).get returns a Promise, and as I use Promise.timeout to re-launch the call every second,
I have a
Promise[Promise[Option[String]]]
So I have to use value.get to have the good type, so it does not seems very clean for the asynchronous aspect.
This code works but my question is : Is there a better way, more elegant, to achieve this? Can I get easily a Promise from another Promise and a Promise.timeout?
Thanks :)
Promise
is a monad, and in general when you find yourself with a nested monad you want to stick a flatMap
in there somewhere. In your case something like this should work:
import akka.util.duration._
import play.api.libs.concurrent._
import play.api.libs.iteratee._
import play.api.libs.ws._
val query = "test"
val url = WS.url("http://search.twitter.com/search.json?q=" + query + "&rpp=1")
val tweets = Enumerator.fromCallback[String](() =>
Promise.timeout(url.get, 1000 milliseconds).flatMap(_.map { response =>
(response.json \\ "text") match {
case Nil => "Nothing found!"
case head :: _ => query + " : " + head.as[String]
}
}.map(Some.apply))
)
I'd personally write it more like this:
val tweets = Enumerator.fromCallback[String](() =>
Promise.timeout(url.get, 1000 milliseconds).flatMap(_.map(
_.json.\\("text").headOption.map(query + " " + _.as[String])
))
)
And not fuss with the "Nothing found!"
message, but depending on what exactly you're doing that might not be appropriate.