Flat structure -> chierarchy

example00.scala

 def comments(postId: Int) : Future[Seq[CommentNode]] = {
    val query = for {
      comment <- Comments if comment.objectId === postId
      author <- Users if author.id === comment.userId
    } yield (author, comment)

    val comments: Future[Seq[Comment]] = for {
      result <- db.run(query.result)
    } yield result.map { case (author, comment) =>
        Comment(comment.id, comment.replyToId, author.name, author.site, comment.date, comment.body, comment.bodyHtml)
    }

    comments.map { m =>

      var newMap: mutable.Map[Int, CommentNode] = mutable.HashMap()
      m.foreach { c =>
        newMap = newMap + (c.id -> CommentNode(c))
      }

      newMap.values.foreach { cm =>
        cm.data.replyToId.foreach { parentId =>
          newMap.get(parentId).foreach { n =>
            cm.parent = Some(n)
            n.children = n.children :+ cm
          }
        }
      }

      newMap.values.filter(_.parent.isEmpty).toSeq
    }
  }