How to use Future[Option] in Scala

[Anil Mathew]

Hi,

  I have a scala application which uses the Slick 3.x for the DB calls. Since all the Slick 3 calls are Async, it returns the Future[Option].

  So I am trying to get the result from a DB call and use that data to do other things. i.e

  

  My DB class has the following code:

  

      // Method to get the User record by username

    def getUserByUsername(username: String): Future[Option[User]] = {

        val query = userData.filter(user => user.username === username)

        val action = query.result.headOption

        db.run(action)

    }

   In my controller, I call the above method and i wanted to use the returned 'User' data for other calls. Can someone please help me how do I do this?

Thanks

[Vlad Patryshev]

The call does not return a User. If you want to apply functions to the value(s) inside, the right solution would be either to use Scala loops, or to use map method, every monad (e.g. Future, Option) has it.

Thanks,
-Vlad

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[Udas]

Vlad is correct. Perhaps you can use the below code as a starting point (copy paste into scala console and play with it).

import scala.concurrent._

import ExecutionContext.Implicits.global

def getUserByUserName(n: String): Future[Option[String]] = Future.successful(Some(n))

def processUser(username: String): Future[Unit] = {

   for {

     optionalUser <- getUserByUserName(username)

     _ = optionalUser map { user =>

        print(s"User is here: ${user}\n")

        // Do whatever you need to do, but say you call a function that is Unit

     } getOrElse {

        print(s"User not found for ${username}\n")

     }

  } yield()

}

val f = processUser("a")

f.value

Hope that helps,

Udas

[Lanny Ripple]

When I work with Play and Databases I really like the technique described by Erik Bakker here

Options in Futures, how to unsuck them

 https://www.youtube.com/watch?v=hGMndafDcc8