making an implicit available within a play action - scala

Question

My app hits many different dbs, which db depends on a query string parameter. I have a DatabaseConfigLocator that takes the string and returns the config and it works great. My problem is I want to make the config for each request available implicitly in my controller. I have tried two approaches.
class MyController extends Controller{
implicit def dbConfig(implicit request: RequestHeader): DatabaseConfig[JdbcProfile] = DatabaseConfigLocator.get[JdbcProfile](request.getQueryString("dbName")
}
This dosn't compile unless I change it to an implicit val with the same type but I need to recheck the query string every request not just once so I don't think an implicit val will work
The other approach was to create an action
object IODBAction extends ActionBuilder[Request]{
def invokeBlock[A](request: Request[A], block: (Request[A]) => Future[Result]) = {
implicit def dbConfig(implicit request: RequestHeader): DatabaseConfig[JdbcProfile] = DatabaseConfigLocator.get[JdbcProfile]("blah")
block(request)
}
}
but that implicit is not available in the scope of the block and I cant find any way to pass it in as an implicit.
My goal is to be able to do something like this
class MyController extends Controller {
def create = {
Action.async {
request =>
ApiResponse {
for {
id <- aProvider.save(validRegistrationRequest.toVisitor)
} yield id
}
}
}
}
class aProvider {
def save(v: Visitor)(implicit dbConfig: DatabaseConfig[JdbcProfile]): ApiResponse[VisitorId]
}
or if the provider can get the implicit at instantiation time all the better
class aProvider(implicit dbConfig: DatabaseConfig[JdbcPRofile]) {
def save(v: Visitor): ApiResponse[VisitorId]
}
Any advice on how to approach this or if its possible with play framework?

Answer 1

Unfortunately, I fear you're stuck with an action receiving a single parameter, so you need to stick to the standard play "Action Composition" pattern. This is documented pretty extensively in the play docs.
I'd define yourself a a "Context" like this:
case class Context(dbConfig: DatabaseConfig[JDBCProfile], request: Request[A])
extends WrappedRequest(request)
Then create a custom action builder like this:
object DBIOAction extends ActionBuilder[Context]{
def invokeBlock[A](request: Request[A], block: (Context[A]) => Future[Result]) = {
val dbConfig = DatabaseConfigLocator.get[JdbcProfile]("blah")
val context = Context(dbConfig, request)
block(context)
}
}
You then should be able to use it like this:
def index = DBIOAction { implicit context =>
// do some stuff. return a result
}
In order to make things simple, I'd pass the implicit context into your service methods, perhaps extracting the dbConfig from the context and passing it the rest of the way down to your DAO's.
class FunService {
def getSomeData(param1: String)(implicit context: Context) = {
// do some work, perhaps using context.dbConfig
}