A grammar-based event logging system in Scala using Lift's Mapper ORM. See the following blog post of a conceptual explanation: http://www.bubblefoundry.com/blog/2010/08/grammar-based-event-logging/

Event.scala

package com.mobtest {
package model {
  
import net.liftweb.mapper._
import net.liftweb.common.{Box, Full, Empty}
  
class Event extends LongKeyedMapper[Event] with IdPK with CreatedUpdated {
  def getSingleton = Event // companion object
   
  object subject extends MappedLong(this)
  object verb extends MappedString(this, 64) {
    override def dbIndexed_? = true
  }
  object directobject extends MappedLong(this) // ie the major object
  object indirectobject extends MappedLong(this) // ie the minor object
   
  def toCC = Event.convert(this)
}
  
object Event extends Event with LongKeyedMetaMapper[Event] {
  // override def fieldOrder = List(subject, verb, directobject, indirectobject)
   
  val BaseEventKey = "BaseEvent"
  val UnknownEventKey = "UnknownEvent"
  val AccountCreatedKey = "AccountCreated"
   
  def convert(event: Event) = event.verb.is match {
    case BaseEventKey => BaseEvent(event.createdAt.is.getTime, Full(event.id))
    case UnknownEventKey => UnknownEvent(event.createdAt.is.getTime, Full(event.id))
    case AccountCreatedKey => AccountCreated(event.subject.is, event.createdAt.is.getTime, Full(event.id))
    case _ => UnknownEvent(event.createdAt.is.getTime, Full(event.id))
  }
}

// base event has a millisecond timestamp
case class BaseEvent(timestamp: Long, id: Box[Long]) {
  def subject: Box[Long] = Empty
  def verb: Box[String] = Full(Event.BaseEventKey)
  def directobject: Box[Long] = Empty
  def indirectobject: Box[Long] = Empty
   
  def toEvent: Event = {
    val e = id.flatMap(Event.findByKey(_)) openOr Event.create
    e.createdAt(new java.util.Date(timestamp))
     
    // optional values
    subject.foreach(s => e.subject(s))
    verb.foreach(v => e.verb(v))
    directobject.foreach(d => e.directobject(d))
    indirectobject.foreach(i => e.indirectobject(i))
     
    // return the Event
    e
  }
   
  def save: Boolean = this.toEvent.save
}

// Catch-all for when we can't match to a more specific event
case class UnknownEvent(override val timestamp: Long, override val id: Box[Long]) extends BaseEvent(timestamp, id) {
  override def verb = Full(Event.UnknownEventKey)
}
  
// account creation events
// user created own account at time
case class AccountCreated(user: Long, override val timestamp: Long, override val id: Box[Long]) extends BaseEvent(timestamp, id) {
  override def subject = Full(user)
  override def verb = Full(Event.AccountCreatedKey)
}

}
}