Using Auto Incrementing fields with PostgreSQL and Slick

Question

How does one insert records into PostgreSQL using AutoInc keys with Slick mapped tables? If I use and Option for the id in my case class and set it to None, then PostgreSQL

Answer 1

I tackled this problem in an different way. Since I expect my User objects to always have an id in my application logic and the only point where one would not have it is during the insertion to the database, I use an auxiliary NewUser case class which doesn't have an id.

case class User(id: Int, first: String, last: String)
case class NewUser(first: String, last: String)

object Users extends Table[User]("users") {
  def id = column[Int]("id", O.PrimaryKey, O.AutoInc)
  def first = column[String]("first")
  def last = column[String]("last")

  def * = id ~ first ~ last <> (User, User.unapply _)
  def autoInc = first ~ last <> (NewUser, NewUser.unapply _) returning id
}

val id = Users.autoInc.insert(NewUser("John", "Doe"))

Again, User maps 1:1 to the database entry/row while NewUser could be replaced by a tuple if you wanted to avoid having the extra case class, since it is only used as a data container for the insert invocation.

EDIT: If you want more safety (with somewhat increased verbosity) you can make use of a trait for the case classes like so:

trait UserT {
  def first: String
  def last: String
}
case class User(id: Int, first: String, last: String) extends UserT
case class NewUser(first: String, last: String) extends UserT
// ... the rest remains intact

In this case you would apply your model changes to the trait first (including any mixins you might need), and optionally add default values to the NewUser.

Author's opinion: I still prefer the no-trait solution as it is more compact and changes to the model are a matter of copy-pasting the User params and then removing the id (auto-inc primary key), both in case class declaration and in table projections.