Inserting a document with reactivemongo and fetching it afterwards - scala

Question

When inserting a value into a persistence layer and returning the result object it is usually a good practice to fetch the newly created entity instead of returning the input data again.
When I try to do this in Scala using reactivemongo I stumble over my language skills.
def create(user: User): Future[User] = {
val newUser = user.createOID()
collection.insert(newUser).map {
case ok if ok.ok => {
for {
createdUser <- this.findOne(BSONDocument("_id" -> newUser._id))
} yield {
createdUser match {
case None => throw new RuntimeException("Could not find just created user")
case Some(x) => x
}
}
}
case error => throw new RuntimeException(error.message)
}
}
Where findOne has the signature:
def findOne(query: BSONDocument): Future[Option[User]]
I get the following error:
[error] found : scala.concurrent.Future[models.User]
[error] required: models.User
[error] createdUser <- this.findOne(BSONDocument("_id" -> newUser._id))
[error] ^
If I return the newUser object everything is fine.
I think I have a general misunderstanding what is happening here - maybe there is a better way to fetch the created object in one shot.

Answer 1

I would say that idiomatic Play/Scala way to do that is the following
def create(user: User): Future[Option[User]] = {
val newUser = user.createOID()
for {
nu <- collection.insert(newUser)
createdUser <- findOne(BSONDocument("_id" -> newUser._id))
} yield {
createdUser
}
}
Notice that this does return Future[Option[User]] and not Future[User] as in your code. I believe that Option[User] is definitely the way to go in this case as it actually tells clients of this method that it's not guaranteed that insertion will succeed (and thus runtime exception is not required as client will do .map on the result of this method — avoid using exceptions if you can deal with them gracefully).
You might also check nu for being ok within yield.