In Anorm is it possible to apply multiple ColumnAliaser to the same query

Question

The scenario is similar to the question at How to better parse the same table twice with Anorm? however the described solutions on that question can no longer be used.

On the scenario where a Message has 2 users I need to parse the from_user and to_user with SQL joins.

case class User(id: Long, name: String)

case class Message(id: Long, body: String, to: User, from: User)

def userParser(alias: String): RowParser[User] = {
    get[Long](alias + "_id") ~ get[String](alias + "_name") map {
        case id~name => User(id, name)
    }
}

val parser: RowParser[Message] = {
    userParser("from_user") ~
    userParser("to_user") ~
    get[Long]("messages.id") ~ 
    get[String]("messages.name") map {
        case from~to~id~body => Message(id, body, to, from)
    }
}

// More alias here possible ?
val aliaser: ColumnAliaser = ColumnAliaser.withPattern((0 to 2).toSet, "from_user.")

SQL"""
SELECT from_user.* , to_user.*, message.* FROM MESSAGE
JOIN USER from_user on from_user.id = message_from_user_id
JOIN USER to_user on to_user.id = message.to_user
"""
.asTry(parser, aliaser)

Answer 1

If I'm right thinking you want to apply multiple ColumnAliaser with different aliasing policies to the same query, it's important to understand that ColumnAliaser is "just" a specific implementation of Function[(Int, ColumnName), Option[String]], so it can be defined/composed as any Function, and is simplified by the factory functions in its companion object.

import anorm.{ ColumnAliaser, ColumnName }

val aliaser = new ColumnAliaser {
  def as1 = ColumnAliaser.withPattern((0 to 2).toSet, "from_user.")
  def as2 = ColumnAliaser.withPattern((2 to 4).toSet, "to_user.")

  def apply(column: (Int, ColumnName)): Option[String] =
    as1(column).orElse(as2(column))
}