Play2 Stackable Action Composition


This module offers Action Composition Utilities to Play2.1, 2.2, 2.3, 2.4, 2.5 applications

Target

This module targets the Scala version of Play2.x

This module has been tested on Play2.5.0

Motivation

Action Composition is somewhat limited in terms of composability.

For example, imagine that we want automatic DB transaction management, auth, and pjax functionality.

def TxAction(f: DBSession => Request[AnyContent] => Future[Result]): Action[AnyContent] = {
  Action.async { request =>
    import TxBoundary.Future._
    DB localTx { session =>
      f(session)(request)
    }
  }
}

def AuthAction(authority: Authority)(f: User => DBSession => Request[AnyContent] => Future[Result]): Action[AnyContent] = {
  TxAction { session => request =>
    val user: Either[Result, User] = authorized(authority)(request)
    user.right.map(u => f(u)(session)(request)).merge
  }
}

type Template = Html => Html
def PjaxAction(authority: Authority)(f: Template => User => DBSession => Request[AnyContent] => Future[Result]): Action[AnyContent] = {
  AuthAction(authority) { user => session => request =>
    val template = if (req.headers.keys("X-Pjax")) views.html.pjaxTemplate.apply else views.html.fullTemplate.apply
    f(template)(user)(session)(request)
  }
}

def index = PjaxAction(NormalUser) { template => user => session => request => 
  val messages = Message.findAll(session)
  Ok(views.hrml.index(messages)(template))
}

So far so good, but what if we need a new action that does both DB transaction management and pjax?

We have to create another PjaxAction.

def PjaxAction(f: Template => DBSession => Request[AnyContent] => Future[Result]): Action[AnyContent] = {
  TxAction { session => request =>
    val template = if (req.headers.keys("X-Pjax")) html.pjaxTemplate.apply else views.html.fullTemplate.apply
    f(template)(session)(request)
  }
}

What a mess!

As an alternative, this module offers Composable Action composition using the power of traits.

Example

1. First step, Create a sub trait of StackableController for every function.

   trait AuthElement extends StackableController with AuthConfigImpl {
       self: Controller with Auth =>
   
     case object AuthKey extends RequestAttributeKey[User]
     case object AuthorityKey extends RequestAttributeKey[Authority]
   
     override def proceed[A](req: RequestWithAttributes[A])(f: RequestWithAttributes[A] => Future[Result]): Future[Result] = {
       (for {
         authority <- req.get(AuthorityKey).toRight(authorizationFailed(req)).right
         user      <- authorized(authority)(req).right
       } yield super.proceed(req.set(AuthKey, user))(f)).merge
     }
   
     implicit def loggedIn(implicit req: RequestWithAttributes[_]): User = req.get(AuthKey).get
   
   }

   trait DBSessionElement extends StackableController {
       self: Controller =>
   
     case object DBSessionKey extends RequestAttributeKey[DBSession]
   
     override def proceed[A](req: RequestWithAttributes[A])(f: RequestWithAttributes[A] => Future[Result]): Future[Result] = {
       import TxBoundary.Future._
       DB.localTx { session =>
         super.proceed(req.set(DBSessionKey, session))(f)
       }
     }
   
     implicit def dbSession(implicit req: RequestWithAttributes[_]): DBSession = req.get(DBSessionKey).get
   
   }

   trait PjaxElement extends StackableController with AuthConfigImpl {
       self: Controller with Auth =>
   
     type Template = Html => Html
   
     case object TemplateKey extends RequestAttributeKey[Template]
   
     override def proceed[A](req: RequestWithAttributes[A])(f: RequestWithAttributes[A] => Future[Result]): Future[Result] = {
       val template = if (req.headers.keys("X-Pjax")) views.html.pjaxTemplate else views.html.fullTemplate
       super.proceed(req.set(TemplateKey, template))(f)
     }
   
     implicit def template(implicit req: RequestWithAttributes[_]): Template = req.get(TemplateKey).get
   
   }

2. mix your traits into your Controller

   object Application extends Controller with PjaxElement with AuthElement with DBSessionElement with Auth with AuthConfigImpl {
   
     def messages = StackAction(AuthorityKey -> NormalUser) { implicit req =>
       val messages = Message.findAll
       Ok(html.messages(messages)(loggedIn)(template))
     }
   
     def editMessage(id: MessageId) = StackAction(AuthorityKey -> Administrator) { implicit req =>
       val messages = Message.findAll
       Ok(html.messages(messages)(loggedIn)(template))
     }
   
   }

3. Mixin different combinations of traits, depending on the functionality that you need.

   object NoAuthController extends Controller with PjaxElement with DBSessionElement {
     
     def messages = StackAction { implicit req =>
       val messages = Message.findAll
       Ok(html.messages(messages)(GuestUser)(template))
     }
   
     def editMessage(id: MessageId) = StackAction { implicit req =>
       val messages = Message.findAll
       Ok(html.messages(messages)(GuestUser)(template))
     }
   
   }

How to use

Add a dependency declaration into your Build.scala or build.sbt file:

libraryDependencies += "jp.t2v" %% "stackable-controller" % "0.6.0"

• for Play2.2.x, use 0.3.0
• for Play2.3.x, use 0.4.1
• for Play2.4.x, use 0.5.1

ExecutionContext

When you want to use scala.concurrent.ExecutionContext, you can use StackActionExecutionContext method.

StackActionExecutionContext returns an ExecutionContext that is given when StackAction method calling. So, users of your StackElement can customize ExecutionContext.

    trait AsyncElement extends StackableController with AuthConfigImpl {
        self: Controller with Auth =>

      private case object FooKey extends RequestAttributeKey[Foo]

      override def proceed[A](req: RequestWithAttributes[A])(f: RequestWithAttributes[A] => Future[Result]): Future[Result] = {
        val ctx: ExecutionContext = StackActionExecutionContext(req)
        val future: Future[Foo] = getFooAsynchronously(ctx)
        future flatMap { 
          foo => super.proceed(req.set(FooKey, foo))(f)
        } recoverWith {
          _ => super.proceed(req)(f)
        }
      }

      implicit def foo(implicit req: RequestWithAttributes[_]): Foo = req.get(FooKey).get

    }

License

This library is released under the Apache Software License, version 2, which should be included with the source in a file named LICENSE.