scala,asynchronous,playframework-2.0 , Play Action Async wrapping a Future


Play Action Async wrapping a Future

Question:

Tag: scala,asynchronous,playframework-2.0

Let's say I have an Action Async block as below in one of my controller:

def myCntr = Action.async { implicit request =>
  // Step 1. .... // look up over the network
  // Step 2. .... // do a database call
}

What would it mean to wrap Step 1 and Step 2 in a Future? Is the Action.async enough to make myCntr calls asynchronous?


Answer:

Action.async is not enough to make your code asynchronous. Here is the signature for async (I picked the simplest overload):

def async(block: => Future[Result]): Action[AnyContent]

It's up to you to provide that Future. If you're calling blocking code you can execute it concurrently like Future { blockingCode() }. However the preferred way is to use futures throughout your application.

A simple action might look something like this:

  def lookup(): Future[Connection] = ???
  def query(c: Connection): Future[QueryResult] = ???

  def myCntr = Action.async {
    for {
      conn <- lookup()
      result <- query(conn)
    } yield NoContent
  }

Related:


Zipping two arrays together with index in Scala?


arrays,scala,zip
I have two arrays populated with integers. They are the same size (val array1 and val array2). I want to fuse them together into tuples with their index as the third element. For example if we have val array1 = Array(5,2,6,2) and val array2 = Array(9,8,3,4) then I want to...

Asynchronously manipulating data from streamReader in F#


asynchronous,f#,streamreader
On the line of Read large txt file multithreaded?, I have the doubt of whether it is equivalent to pass to each thread an sliced chunk of a Seq and whether it will safely handle the paralellism; is it StreamReader thread-safe? Here is the code I am using to test...

Scala string replacement of entire words that comply with a pattern


string,scala,scala-collections,scala-string
In a string, how to replace words that start with a given pattern ? For instance replace each word that starts with "th", with "123", val in = "this is the example, that we think of" val out = "123 is 123 example, 123 we 123 of" Namely how to...

Scala - Option Type Var Manipulation


scala,scala-option
I am working on an online exercise practicing Options and threads, both of which I have very little experience. The online exercise comes with a test suite, so right now I am trying to get my Option test cases to pass before I move on to the thread test cases....

ZeroMQ pattern for multiple asynchronous requests to single endpoint


sockets,asynchronous,zeromq
I'm using zmq to develop a distributed application having the following network topology: a client node that initiates a request and a server node that replies to requests. Since the client is a node.js application I can't block after a send call to wait the response, so the scenario is...

Async await usage for MongoDB repository


c#,mongodb,asynchronous,parallel-processing,async-await
I have a MongoDB repository class as you see below: public class MongoDbRepository<TEntity> : IRepository<TEntity> where TEntity : EntityBase { private IMongoClient client; private IMongoDatabase database; private IMongoCollection<TEntity> collection; public MongoDbRepository() { client = new MongoClient(); database = client.GetDatabase("Test"); collection = database.GetCollection<TEntity>(typeof(TEntity).Name); } public async Task Insert(TEntity entity) { if...

Scala first program issue


scala,recursion,case,frequency
I have just started to learn Scala after some experience with functional programming in other languages. def freq(c:Char, y:String, list:List[(Char,Int)]): List[(Char,Int)] = list match{ case _ => freq(c, y.filter(_ == c), list :: List((count(c,y),c))) case nil => list } In the above code I am getting an error when trying...

Implicit Generic.Aux missing on conversion from Shapeless HList to case class


scala,shapeless,type-level-computation
I just recently started learning scala and today I decided I wanted to write a CSV parser that would load nicely into case classes but store the data in rows (lists) of Shapeless's HList object so that I could get some exposure to type-level programming. Here's what I have so...

Retrieving TriangleCount


scala,apache-spark,spark-graphx
I'm trying to retrieve the amount of triangles from a graph using graphX. As I'm new to both Scala and graphX, I'm currently quite stuck. I'm creating a graph from an edgefile: 1 2 1 3 2 3 This should be 1 triangle. Next I'm using the build in function...

Scala (Slick) HList splitting to case classes


scala,slick
currently I have a HList with more than 22 fields and now I want to split it to 2-3 case classes, is there an easy functional way to do it? Currently I use the following syntax: CaseClass1(c.head, c.tail.head, c.tail.tail.head, etc...) However that doesn't seem to be right since I have...

Scala slf4j dynamic file name


scala,logging,slf4j
I just successfully added Grizzled-SLF4J logger to my project using this link http://alvinalexander.com/scala/how-to-log-output-file-grizzled-slf4j-scala-simplelogger.properties But using this properties, there is no option to create dynamic file name: org.slf4j.simpleLogger.logFile = /tmp/myapp.log org.slf4j.simpleLogger.defaultLogLevel = info org.slf4j.simpleLogger.showDateTime = true org.slf4j.simpleLogger.dateTimeFormat = yyyy'/'MM'/'dd' 'HH':'mm':'ss'-'S org.slf4j.simpleLogger.showThreadName = true...

Why is the task is not cancelled when I call CancellationTokenSource's Cancel method in async method?


c#,asynchronous,task,cancellationtokensource,cancellation-token
I created a small wrapper around CancellationToken and CancellationTokenSource. The problem I have is that the CancelAsync method of CancellationHelper doesn't work as expected. I'm experiencing the problem with the ItShouldThrowAExceptionButStallsInstead method. To cancel the running task, it calls await coordinator.CancelAsync();, but the task is not cancelled actually and doesn't...

implicit resolution for a function argument


scala,implicit,context-bound
I tried to implement mergesort in Scala. I got to the following: def mergeSort[A: Ordering](as: List[A]): List[A] = as match { case Nil => as case head :: Nil => as case _ => { val (l, r) = split(as) merge(mergeSort(l), mergeSort(r)) } } def split[A](as: List[A]): (List[A], List[A]) =...

How to instantiate lexical.Scanner in a JavaTokenParsers class?


scala,parsing,lexical-scanner
I am writing a parser which inherits from JavaTokenParsers in that I have a function as follow: import scala.util.parsing.combinator.lexical._ import scala.util.parsing._ import scala.util.parsing.combinator.RegexParsers; import scala.util.parsing.combinator.syntactical.StdTokenParsers import scala.util.parsing.combinator.token.StdTokens import scala.util.parsing.combinator.lexical.StdLexical import scala.util.parsing.combinator.lexical.Scanners import scala.util.parsing.combinator.lexical.Lexical import...

Operand order in Scala List.prepend (::)


list,scala,operators
Odersky has brilliantly optimized Java syntax, enabling object calls without dots and parenthesis. I.e. instead of list.prepend(item), you now simply write list :: item, which also turns language operators into simple object methods. Here, List defines :: (prepend) operator. However, you normally write it vice-verse in Scala, using item ::...

Access key from mapValues or flatMapValues?


scala,apache-spark
In Spark 1.3, is there a way to access the key from mapValues? Specifically, if I have val y = x.groupBy(someKey) val z = y.mapValues(someFun) can someFun know which key of y it is currently operating on? Or do I have to do val y = x.map(r => (someKey(r), r)).groupBy(_._1)...

Like clause not working with int column in slick


scala,slick,slick-2.0
Slick doesn't seem to support like clauses on int columns. The following code where Status.code is of int type doesn't seem to work. Would there be a workaround for this? val query = for { s <- Status if s.code like "1%" } yield (s) ...

SCALA: change the separator in Array


arrays,string,scala,delimiter
I have an Array like this. scala> var x=Array("a","x,y","b") x: Array[String] = Array(a, x,y, b) How do I change the separator comma in array to a :. And finally convert it to string like this. String = "a:x,y:b" My aim is to change the comma(separators only) to other separator(say,:), so...

ZipList with Scalaz


list,scala,scalaz,applicative
Suppose I have a list of numbers and list of functions to apply to numbers: val xs: List[Int] = List(1, 2, 3) val fs: List[Int => Int] = List(f1, f2, f3) Now I would like to use an Applicative to apply f1 to 1, f2 to 2, etc. val ys:...

Implementing map on a tree using fold


scala,haskell
I am trying to implement a map using fold. I could do so in Haskell data Tree a = EmptyTree | Node a (Tree a) (Tree a) deriving (Show) foldTree :: Tree a -> b -> (b -> a -> b -> b) -> b foldTree EmptyTree d _ =...

Scala unapplySeq extractor syntax


scala,pattern-matching,scala-2.11
I (inadvertently) came across a bit of pattern matching syntax I did not expect to compile and now cannot figure out. It appears related to unapplySeq. Note the case x List(_,_) part in this simple example: val xs = List(1, 2, 3) //> xs : List[Int] = List(1, 2, 3)...

refer to scala function by name?


scala
Here is another stupid scala question regarding functions as first class objects in Scala. I'm very sorry if this is a repeat, as it probably is. In Python, Lisp, Perl, Scheme, etcetera I'm used to creating function values and assigning them names and passing them around to other functions, like...

Play Framework Form Error Handling


scala,playframework,playframework-2.3,playframework-2.4
This is my view file containing the form that has to filled in by the user: @helper.form(call) { @helper.input(resumeForm("surname"), '_label -> "Surname") { (id, name, value, args) => <input name="@name" type="text" value="@value" placeholder="Enter your surname"> } } This is my custom field constructor: @(elements: helper.FieldElements) @if(!elements.args.isDefinedAt('showLabel) || elements.args('showLabel) == true)...

Spray route get response from child actor


scala,akka,spray
I am trying to figure out how I can setup a Master Actor that calls the appropriate children, in support of some spray routes where I am trying to emulate db calls. I am new to akka / spray, so just trying to gain a better understanding of how you...

Call method after asynchronous request obj-c


ios,objective-c,asynchronous,uiviewcontroller,nsobject
In my app I init a new object, where there is method which calls NSURLConnection's sendAsynchronousRequest method. After the request, I would like to call a method in the caller UIViewController. I tried to use a static method but I then I can't control IBOutlets. How can I do this?...

How to unmarshall akka http request entity as string?


json,scala,akka-http
I'm trying to unmarshall request payload as string, but for some reason it's failing. My code: path("mypath") { post { decodeRequest { entity(as[String]) {jsonStr => //could not find implicit value for...FromRequestUnmarshaller[String] complete { val json: JsObject = Json.parse(jsonStr).as[JsObject] val jsObjectFuture: Future[JsObject] = MyDatabase.addListItem(json) jsObjectFuture.map(_.as[String]) } } } } } In...

How to effectively get indices of 1s for given binary string using Scala?


scala,functional-programming,higher-order-functions
Suppose we have a binary string such as 10010010. All I want is a function returning indices of 1s for that string: indicesOfOnes("10010010") -> List(0, 3, 6) indicesOfOnes("0") -> List() And what I implemented is: def indicesOfOnes(bs: String): List[Int] = { val lb = ListBuffer[Int]() bs.zipWithIndex.foreach { case (v, i)...

Type to impose required constrains on a double


scala,implicit-conversion
I would like to have a run time check on a Double, without having to scatter the check all over my code. I thought that defining an implicit class would do the job, something on the line: implicit class Probability(val x: Double) { require(x >= 0.0 && x <= 1.0,...

How should I execute functions only one after another in JavaScript?


javascript,asynchronous,synchronous
I am trying to make a time conversion tool, first thing it does is gets the co-ordinates of both the cities you enter and then calculates time accordingly. But the problem I am facing is that the function which gets the co-ordinates takes some time and it is asynchronous as...

PlayFramework: value as is not a member of Array[Byte]


scala,playframework
I want to make file download from a database using Play framework. But when I use this code I get this message: value as is not a member of Array[Byte] And if I change Ok(bytOfImage.as("image/jpg")) to Ok(bytOfImage) it works good but I get a file with a name: secondindex without...

My Scala program won't print anything


scala
Basically I'm trying to write a program that has a list of books and authors and then prints 2 things out, res1, which should print the book titles of the authors that have the name "Andrei" in it and res2 that should print the book titles that have the string...

Call Sync method call from Async Callback?


c#,asynchronous,synchronous
What happens when a synchronous method is called within an asynchronous callback? Example: private void AcceptCallback(IAsyncResult AR) { tcp.BeginReceive(ReceiveCallback); } private void ReceiveCallback(IAsyncResult AR) { tcp.Send(data); } A connection is accepted and the async receive callback is started. When the tcp connection receives data, it calls the receive callback. If...

Spray microservice assembly deduplicate


scala,sbt,akka,spray,microservices
I'm using this template to develop a microservice: http://www.typesafe.com/activator/template/activator-service-container-tutorial My sbt file is like this: import sbt._ import Keys._ name := "activator-service-container-tutorial" version := "1.0.1" scalaVersion := "2.11.6" crossScalaVersions := Seq("2.10.5", "2.11.6") resolvers += "Scalaz Bintray Repo" at "https://dl.bintray.com/scalaz/releases" libraryDependencies ++= { val containerVersion = "1.0.1" val configVersion = "1.2.1"...

Preventing a class instantiation in Scala using Factory Pattern [duplicate]


scala,factory-pattern
This question already has an answer here: How to check constructor arguments and throw an exception or make an assertion in a default constructor in Scala? 2 answers Suppose that I have the following class defined in Scala: class ClassA(val n: Int) { ... } I want to limit...

How to use the Akka ask pattern without blocking


scala,asynchronous,akka,future
Hi I have a actor which is responsible for fetching data from a database, turning it into a list and sending it back to the sender. I am using the ask pattern to receive response from my actor, because I don't want to use await.result because this approach will block...

Calling a function from outside of require which is written inside of require in dojo


javascript,html,asynchronous,dojo
<html> <head> <script> require(["dojo/ready"],function(ready){ function init(dataItem) { alert("inside init method") updateData(dataItem); } function updateData(dataItem){ //inside this function, i am creating some breadcrumb and making each part of it a link. //Now that link is calling another method outerFunction() } ready(function(){ init({ type: "All Locations", id: "All_Locations" }); }); }); function...

Collapse similar case statements in Scala


scala,functional-programming,pattern-matching
Is there an elegant way to do something like the following example using just one case statement? foobar match { case Node(Leaf(key, value), parent, qux) => { // Do something with parent & qux } case Node(parent, Leaf(key, value), qux) => { // Do something with parent & qux (code...

Scodec: Coproducts could not find implicit value for parameter auto: scodec.codecs.CoproductBuilderAuto


scala,scodec
I am trying to define an Scodec coproduct codec for communicating with an EELink GPS. Here is the code: import scodec.Codec import scodec.bits.ByteVector import scodec.codecs._ trait Message object Message { implicit val discriminated: Discriminated[ Message, Int ] = Discriminated(uint8) val codec: Codec[ Message ] = Codec.coproduct[ Message ].discriminatedByIndex(uint8) } case...

Bulkheading strategies for Akka actors


java,asynchronous,akka,blocking,future
I have a scenario where an important actor needs to make a call to a slow (15 - 20 seconds) remote system: // Non-actor code equivalent public Result makeSlowNetworkCall(Request request) { Result result = slowServiceClient.soooooSlow(request); // Could be up to 15 - 20 SECONDS (mehhhh) return result; } The Akka...

Scala running issue on eclipse


eclipse,scala
I configured everthing within eclipse for scala. I create a snippet to show you the issue, i can't see in run options run as scala application, i also tried to find my main class under build configuration option but i can't find it. How i can solve it?...

Contexts and callbacks from asynchronous tasks


android,android-fragments,asynchronous
I've been experiencing this problem on some devices, especially Samsung. I have an activity that has 7 fragments. In most of them, I start an async task for getting some data. I handle the exceptions by creating a handler in onCreateView(). handler = new Handler(new Handler.Callback() { @Override public boolean...

How to define a Regex in StandardTokenParsers to identify path?


regex,scala,parsing,lexical-analysis
I am writing a parser in which I want to parse arithmetic expressions like: /hdfs://xxx.xx.xx.x:xxxx/path1/file1.jpg+1 I want to parse it change the infix to postfix and do the calculation. I used helps from a part of code in another discussion as well. class InfixToPostfix extends StandardTokenParsers { import lexical._ def...

Is this definition of a tail recursive fibonacci function tail-recursive?


scala,f#,functional-programming,tail-recursion,continuation-passing
I've seen around the following F# definition of a continuation-passing-style fibonacci function, that I always assumed to be tail recursive: let fib k = let rec fib' k cont = match k with | 0 | 1 -> cont 1 | k -> fib' (k-1) (fun a -> fib' (k-2)...

Scala rep separator for specific area of text


scala,parser-combinators
Imaging i've got following: --open Client: enter Nick Age 28 Rosewell, USA Client: enter Maria Age 19 Cleveland, USA --open-- I need a result close to the following: List(List(Nick, Age 28, Rosewell), List(Maria, Age19, Cleveland)) It can be as many clients inside open body as you can imagine, so the...

Convert RDD[Map[String,Double]] to RDD[(String,Double)]


scala,apache-spark,rdd
I did some calculation and returned my values in a RDD containing scala map and now I want to remove this map and want to collect all keys values in a RDD. Any help will be appreciated....

Future yielding with flatMap


scala
Given Futures fa, fb, fc, I can use f: Function1[(A,B,C), Future[D]], to return a Future[D] either by: (for { a <- fa b <- fb c <- fc } yield (a,b,c)).flatMap(f) which has the unenviable property of declaring the variables a,b,c twice. or a.zip(b).zip(c).flatMap{ case (a, (b, c)) => f(a,...

How to generalize the round methods


scala
I have the following four methods, using BigDecimal to round a number: private def round(input: Byte, scale: Int): Byte = { BigDecimal(input).setScale(scale, RoundingMode.HALF_UP).byteValue() } private def round(input: Short, scale: Int): Short = { BigDecimal(input).setScale(scale, RoundingMode.HALF_UP).shortValue() } private def round(input: Int, scale: Int): Int = { BigDecimal(input).setScale(scale, RoundingMode.HALF_UP).intValue() } private def...

Passing a function foreach key of an Array


scala,apache-spark,scala-collections,spark-graphx
I have an array like that : val pairs: Array[(Int, ((VertexId, Seq[Int]), Int))] which generates this output : (11,((11,ArraySeq(2, 5, 4, 5)),1)) (11,((12,ArraySeq(7, 7, 8, 2)),1)) (11,((13,ArraySeq(5, 9, 8, 7)),1)) (1,((1,ArraySeq(1, 2, 3, 4)),1)) (1,((4,ArraySeq(1, 5, 1, 1)),1)) I want to build a Graph for each pairs._1. That means for...

ElasticSearch asynchronous post


database,post,asynchronous,elasticsearch,get
I'm posting data on my ElasticSearch database. I've noticed that data is not immediately available, it requires some milliseconds to show up in a GET request. I can live with that (after all, the calls are asynchronous so this behavior is expected) but in my test code I need to...