MongoDB with scala and casbah

ManageCities.scala

package models.nereida

import scala.collection.mutable.ArrayBuffer
import com.mongodb.casbah.Imports._
import scala.collection.JavaConversions._
import org.bson.types.ObjectId

trait ManageCities {

	def addCity(city:City):City = {
		val newState = city.state + ("_id" -> new ObjectId())
		citiesCollection += newState
		City(newState)
	}

	def cities():List[City] = {
		val list:ArrayBuffer[City] = new ArrayBuffer[City]();
		citiesCollection.find.foreach { cada => list += City(cada) }
		list.toList
	}

	def findCityById(id:String):Option[City] = {
		citiesCollection.findOneByID(id).map { city =>
			Some[City](City(city))
		}.getOrElse {
			Some[City](null)
		}
	}

	def removeCityById(id:String):Option[City] = {
		findCityById(id).map { city => 
			citiesCollection.remove(city.state)
			Some(city)
		}.getOrElse {
			Some[City](null)
		}
	}

	def updateCityById(id:String, name:String):Option[City] = {
		findCityById(id).map { city => 
			city.state.put("name", name)
			citiesCollection.save(city.state)
			Some(city)
		}.getOrElse {
			Some[City](null)
		}
	}

	def mongoConnection(): MongoConnection = MongoConnection("host")

	def mongoDB(): MongoDB = {
		val mongodb:MongoDB = mongoConnection()("nereida")
		mongodb.authenticate("user", "pwd")
		mongodb
	}

	def citiesCollection(): MongoCollection = {
		mongoDB()("cities")
	}

	implicit def dbObjectToMap(dbObject:DBObject): Map[String,AnyRef] = {
		dbObject.toMap.asInstanceOf[Map[String,AnyRef]]
	}

	implicit def map2DBObject(state:Map[String,AnyRef]): DBObject = {
		MongoDBObject(state.toList).asDBObject
	}
}