Handling errors in ReactiveMongo - scala

Question

I am working on a simple RESTful web service using Play Framework 2.1.5 and ReactiveMongo 0.9 using ReactiveMongo Play plugin. It has been a long time since I used Play Framework for the last time. I am trying to insert a document using:
def create = Action(parse.json) { request =>
Async {
val coll = db.collection[JSONCollection](...)
val obj = Json.obj(
"username" -> ...,
...
)
users.insert(obj).map { err => err match {
case e if !e.ok => InternalServerError(Json.obj("result" -> 0, "error" -> e.message))
case _ => Ok(Json.obj("result" -> 1))
}}
}
}
I have expected that once the query execution fails (e.g. due to the duplicate value in an index), I will handle it without any problem. But it is working differently - in case of failure a DatabaseException is thrown instead of satisfying the Promise[LastError] with an appropriate value. What am I missing please?

Answer 1

When an exception happens in a future any calls to map will be ignored and the exception will be passed along the chain of futures.
Explicitly handling the exceptions in a chain of Futures can be done with recover and recoverWith. You can read more about it in the overview of futures in the scala-lang docs:
http://docs.scala-lang.org/overviews/core/futures.html#exceptions

Answer 2

Try this code-
def insert(coll: BSONCollection, doc: BSONDocument): Future[Unit] = {
val p = Promise[Unit]
val f = coll.insert(doc)
f onComplete {
case Failure(e) => p failure (e)
case Success(lastError) => {
p success ({})
}
}
p.future
}

Answer 3

I hope this simplifies your need...
def create = Action (parse.json) { request =>
Async {
val coll = db.collection[JSONCollection](...)
val obj = Json.obj ("username" -> ...)
users.insert(obj).map {
case ins if ins.ok => OK (...)
case ins => InternalServerError (...)
} recover {
case dex: DatabaseException =>
log.error(..)
InternalServerEror(...)
case e: Throwable =>
log.error (..)
InternalServerError (...)
}
}
}