Slick - What if database does not contain result - scala

Question

I am trying to build a simple RESTful service that performs CRUD operations on a database and returns JSON. I have a service adhering to an API like this
GET mydomain.com/predictions/some%20string
I use a DAO which contains the following method that I have created to retrieve the associated prediction:
def getPrediction(rawText: String): Prediction = {
val predictionAction = predictions.filter{_.rawText === rawText}.result
val header = predictionAction.head
val f = db.run(header)
f.onComplete{case pred => pred}
throw new Exception("Oops")
}
However, this can't be right, so I started reading about Option. I changed my code accordingly:
def getPrediction(rawText: String): Option[Prediction] = {
val predictionAction = predictions.filter{_.rawText === rawText}.result
val header = predictionAction.headOption
val f = db.run(header)
f.onSuccess{case pred => pred}
None
}
This still doesn't feel quite right. What is the best way to invoke these filters, return the results, and handle any uncertainty?

Answer 1

I think the best way to rewrite your code is like this:
def getPrediction(rawText: String): Future[Option[Prediction]] = {
db.run(users.filter(_.rawText === rawText).result.headOption)
}
In other words, return a Future instead of the plain result. This way, the database actions will execute asynchronously, which is the preferred way for both Play and Akka.
The client code will then work with the Future. Per instance, a Play action would be like:
def prediction = Action.async {
predictionDao.getPrediction("some string").map { pred =>
Ok(views.html.predictions.show(pred))
}.recover {
case ex =>
logger.error(ex)
BadRequest()
}
}