Scala Play 2 Guice dependency injection with traits

Question

In my application I have the following traits/concrete classes:

In package models.daos :

trait UserDAO // UserDAO.scala
class UserDAOImpl @Inject() (app: play.api.Appliction) extends UserDAO // UserDAOImpl.scala

In package controllers :

class Application @Inject() (userDao: UserDAO) extends Controller

However, when I run the app I get:

ProvisionException: Unable to provision, see the following errors:

1) No implementation for models.daos.UserDAO was bound.
  while locating models.daos.UserDAO
    for parameter 0 at controllers.Application.<init>(Application.scala:15)
  while locating controllers.Application
    for parameter 1 at router.Routes.<init>(Routes.scala:31)
  while locating router.Routes
  while locating play.api.inject.RoutesProvider
  while locating play.api.routing.Router

I'm new to dependency injection and don't really know how to tell Guice to use the concrete class.

Answer 1

You need to extend AbstractModule

class DaoModule extends AbstractModule {
  def configure() = {
    bind(classOf[UserDAO])
     .to(classOf[UserDAOImpl])
  }
}

in conf/application.conf you need to add:

play.modules.enabled += "modules.DaoModule"

Answer 2

You need to create injector somewhere in your code, typically in Global object of your Play module:

object Global extends GlobalSettings {

  val injector = Guice.createInjector(
    new AbstractModule {
      protected def configure() = {
        bind(classOf[UserDAO]).to(classOf[UserDAOImpl])
      }
    }
  )
  ...
}