Filtering in Slick with foreign key field

Question

Is it possible to use a foreign key field in a Slick where or filter statement?

Something like (where the user field is a foreign key to a Table for which User is its mapped projection) (this does not compile):

def findByUser(user: User)(implicit s: Session): Option[Token] =
    tokens.where(_.user === user).firstOption

Or should we use the foreign key explicitely?

def findByUser(user: User)(implicit s: Session): Option[Token] =
    tokens.where(_.userId === user.id).firstOption

Answer 1

Yes, ids are good.

def findByUserId(userId: Long)(implicit s: Session): Option[Token] =
    tokens.filter(_.userId === userId).firstOption

findByUserId( user.id )

This allows the method to be used, even when the only thing you have is an id. Slick deliberately exposes the relational model (with a functional touch) and does not hide it, among other reasons because using id's instead of object references allows to refer to rows that are not loaded into memory merely by their id.

Or even better and simpler, because built into Slick:

val findByUserId = tokens.findBy(_.userId) // pre-compiles SQL for better performance
findByUserId(user.id).firstOption