[Solved]-How to Design and Call Scala API with Futures-scala

Generally when working with Futures, you'll want to do any further processing via methods called on the returned Future. Eg.:

val newUser = User(7, "someName")
val future = userRepo.insertOrUpdate(newUser)
future.onSuccess { outcome => // Here, 'outcome' will hold whatever was contained in the Future - Unit in your description above.
   val storedUser = userRepo.findById(7) // This will only execute once the future completes (successfully).
   ...
}

There are plenty of other useful methods for manipulating a Future (or a collection of them), such as "onFailure", "recover", "map" and "flatMap".

Try not to wait on the Future until as late as possible - preferably let Play or Spray or whatever other framework you might happen to be using take care of it for you (see here for Play documentation on doing this, for example).

Finally, in terms of your DB call to insert, I'd look into having the call return at least a boolean, or better still the primary key the new entry was inserted with, rather than Unit.