Is there a more idiomatic way to use Casbah to check a password?

Question

I have the following code:

def authenticateByUsername(username: String, password:String): Boolean = {
    val user = users.findOne(MongoDBObject(USERNAME -> username))
    if(user.isDefined){
        val pw = user.get.getAs(PASSWORD)
        if(pw.isDefined) 
            BCrypt.checkpw(pw.get, password)
        else false
    }else false
}

Is there a more idiomatic way of doing this? It's an if-else nightmare, which just doesn't seem right in Scala.

Answer 1

You're correct that there's a better way, and in general using get (or, to a slightly lesser degree, isDefined) on an Option is a red flag. In this case you can use a for-comprehension:

def authenticateByUsername(username: String, password: String): Boolean = {
  val result: Option[Boolean] = for {
    user <- users.findOne(MongoDBObject(USERNAME -> username))
    pass <- user.getAs(PASSWORD)
  } yield BCrypt.checkpw(pass, password)

  result getOrElse false
}

Or, a little more concisely:

def authenticateByUsername(username: String, password: String): Boolean =
  users.findOne(MongoDBObject(USERNAME -> username)).flatMap(
    _.getAs(PASSWORD)
  ).map(
    BCrypt.checkpw(_, password)
  ).getOrElse(false)

The latter is essentially just a desugared version of the for-comprehension.