SlickRepository.scala

trait EntityBase {
  def id: String
}

trait Repository {
  type Entity <: EntityBase

  def get(id: String): Option[Entity]
}

trait SlickRepository extends Repository {
  val profile: scala.slick.driver.JdbcProfile
  def database: profile.simple.Database

  import profile.simple._

  abstract class BaseTable(tag: Tag, tableName: String) extends Table[Entity](tag, tableName) {
    def id: Column[String]
  }

  val table: TableQuery[BaseTable]  // needs to be covariant

  override def get(id: String): Option[Entity] = database.withSession { implicit session =>
    table.filter(_.id === id).list.headOption
  }

}

case class User(id: String, name: String, email: String) extends EntityBase

abstract class UserRepository extends SlickRepository {

  type Entity = User

  import profile.simple._

  class UserTable(tag: Tag) extends BaseTable(tag, "user") {
    def id = column[String]("userid", O.PrimaryKey, O.AutoInc)
    def name = column[String]("name")
    def email = column[String]("email")

    def * = (id, name, email) <> (User.tupled, User.unapply)
  }

  val table:TableQuery[BaseTable] = TableQuery[UserTable]
}

Error:(45, 7) overriding value table in trait SlickRepository of type UserRepository.this.profile.simple.TableQuery[UserRepository.this.BaseTable];
value table has incompatible type
val table = TableQuery[UserTable]
^

info] Compiling 1 Scala source to /Users/pedrofurla/dev/projects/slick/slick-perf/target/scala-2.10/classes...
[error] /Users/pedrofurla/dev/projects/slick/slick-perf/src/main/scala/slickperf/irc.scala:45: type mismatch;
[error] found : scala.slick.lifted.TableQuery[UserRepository.this.UserTable]
[error] required: UserRepository.this.profile.simple.TableQuery[UserRepository.this.BaseTable]
[error](which expands to) scala.slick.lifted.TableQuery[UserRepository.this.BaseTable]
[error] Note: UserRepository.this.UserTable <: UserRepository.this.BaseTable, but class TableQuery is invariant in type E.
[error] You may wish to investigate a wildcard type such as _ <: UserRepository.this.BaseTable. (SLS 3.2.10)
[error] val table:TableQuery[BaseTable] = TableQuery[UserTable]
[error] ^

  import scalaz.syntax.traverse._
  import scalaz.std.AllInstances._ // IDEA says it's not used, but it's a lie

  val rs: List[List[Throwable \/ Report]] = ls map { _.sequence } // IDEA says it's an error, it's not!
  val rs2 : List[Throwable \/ List[Report]] =  rs.transpose map { _.sequenceU }

Have you found a way to get around this? I'm struggling with a way to come up with a base repository like this, running into those same "value table has incompatible type" errors.