Using guice when creating a custom Action using ActionBuilder in play

Question

How can I use guice when creating a custom Action using ActionBuilder?

It seems to complain with "not found: value MyAction" if I change the ActionBuilder from a object to a class.

I have this but it doesn't work:

case class MyModel(name: String, request: Request[A]) extends WrappedRequest[A](request)

class MyAction @Inject()(userService: UserService) extends ActionBuilder[MyModel] {
  def invokeBlock[A](request: Request[A], block: (MyModel[A]) => Future[SimpleResult]) = {
    val abc = loadAbc(request)
    block(new MyModel(abc, request))
  }

  def loadAbc(rh: RequestHeader): String {
    "abc" // just for testing
  }
}

So changing it from an object to a class causes it to fail, and I tried keeping it as an object but then it doesn't compile correctly.

How can I get this to work?

I have it working just fine in my controllers.

Answer 1

With a few minor corrections, what you've got seems to work already. All you've got to do is inject the guice-instantiated instance of MyAction into your controller, and then you can use the instance (rather than trying to use the MyAction class name).

This works with Play 2.3:

import scala.concurrent.Future
import javax.inject.{Inject, Singleton}
import play.api.mvc._

class UserService() {
  def loadAbc(rh: RequestHeader) = "abc"
}

class MyModel[A](val name: String, request: Request[A]) extends WrappedRequest[A](request)

class MyAction @Inject()(userService: UserService) extends ActionBuilder[MyModel] {
  def invokeBlock[A](request: Request[A], block: (MyModel[A]) => Future[Result]) = {
    val abc = userService.loadAbc(request)
    block(new MyModel(abc, request))
  }
}

@Singleton
class Application @Inject() (myAction: MyAction) extends Controller {
  def index = myAction { request =>
    Ok(request.name)
  }
}

You can't use object because that violates the design of Guice. object is a singleton instantiated by Scala itself and cannot have instance variables, whereas Guice needs to be able to instantiate classes on the fly so that it can inject dependencies.

Answer 2

I think your code should work if you use it like this:

class MyClass @Inject()(myAction: MyAction) {
  val echo = myAction { request =>
    Ok("Got request [" + request + "]")
  }
}