SORM Persisted 'id' undefined - scala

Question

I am just trying to learn SORM and am playing with what I think is some simple sample code. To whit:
case class Book(var author:String, var title:String);
object Db extends Instance(
entities = Set(Entity[Book]()),
url = "jdbc:h2:mem:test",
user = "",
password = "",
initMode = InitMode.Create
)
And then:
val b : Book with Persisted = Db.save( Book("foo","bar") )
When attempting to compile this, I get:
[error] /Users/rjf/IdeaProjects/PlayTest/app/controllers/Application.scala:22: type mismatch;
[error] found : models.Book
[error] required: sorm.Persisted with models.Book
[error] val b : Book with Persisted = Db.save( Book("foo","bar") )
[error] ^
If I change the Book declaration to:
case class Book(var author:String, var title:String) extends Persisted;
I then get:
[error] /Users/rjf/IdeaProjects/PlayTest/app/models/Book.scala:17: class Book needs to be abstract, since:
[error] it has 2 unimplemented members.
[error] /** As seen from class Book, the missing signatures are as follows.
[error] * For convenience, these are usable as stub implementations.
[error] */
[error] def id: Long = ???
[error] def mixoutPersisted[T]: (Long, T) = ???
[error] case class Book(var author:String, var title:String) extends Persisted;
[error] ^
Apologies for the newbie question. No doubt that the fact I'm learning Scala at the same time is a contributing factor.

Answer 1

To solve your issue, just remove the explicit type annotation:
val b = Db.save( Book("foo","bar") )
Don't worry, you'll still be able to access the same interface as Book with Persisted.
As to why this happens, this seems to be a bug of Scala, and it's been reported.
A sidenote
Don't use vars in case class declaration. Immutability is the whole point of case classes. The correct declaration would be:
case class Book(author:String, title:String)
which is the same as
case class Book(val author:String, val title:String)