基本的には実装詳細を隠蔽しつつDBに入れる時など限定で値を取り出す方法

foo.scala

case class Foo(value: Int)
case class Bar(value: String)
case class Baz(private val foo: Foo, private val bar: Bar) {
  def fooBar: String = foo.value.toString + bar.value 
}

val baz = Baz(Foo(1), Bar("bar"))

scala> Baz.unapply
case def unapply(x$0: Baz): Option[(Foo, Bar)]