Enumerations -> Sealed trait with a "Value"?

Question

This question is related to the first one: Iteration over a sealed trait in Scala?

I have the following sealed trait

/**
 * @author Sebastien Lorber (<i>lorber.sebastien@gmail.com</i>)
 * Date: 02/12/12 - Time: 17:49
 */
sealed trait ResizedImageKey {

  /**
   * Get the dimensions to use on the resized image associated with this key
   */
  def getDimension(originalDimension: Dimension): Dimension

}

object ResizedImageKey {
  val ALL_KEYS: List[ResizedImageKey] = List(Large,Medium,Small,X2)
}

case class Dimension(width: Int,  height: Int)

case object Large extends ResizedImageKey {
  def getDimension(originalDimension: Dimension) = Dimension(1000,1000)
}

case object Medium extends ResizedImageKey{
  def getDimension(originalDimension: Dimension) = Dimension(500,500)
}

case object Small extends ResizedImageKey{
  def getDimension(originalDimension: Dimension) = Dimension(100,100)
}

case object X2 extends ResizedImageKey{
  def getDimension(originalDimension: Dimension) = Dimension(
    width = originalDimension.width * 2,
    height = originalDimension.height * 2
  )
}

This works fine for now. The matter is that I need to be able to use my ResizedImageKey as a key for a map that will be stored in MongoDB with Salat.

I don't think Salat support "sealed trait convertion" right? So should I move to Enumeration, which forces me to do a match / case for the dimensions computations? Or is there any known solution to this problem? Is it possible to create enumeration Value object without extending Enumeration or something?

Thanks

You do get a "match is not exhaustive ..." warning as expressed, because the trait is sealed. — yakshaver, Dec 04 '12 at 04:49

score 3 · Accepted Answer · answered Dec 03 '12 at 21:46

3

Salat developer here.

Salat supports case object hierarchies using the @Salat annotation. (I never recommend using enums in Scala - they're dreadful.)

Now... using a case object as the key for a map is actually not something that mongo supports. All map keys in mongo need to be strings.

So what does this map you're trying to persist look like?

answered Dec 03 '12 at 21:46

prasinous

798
3
6

Thanks. It looks like [ImageResizeKey,FileDescriptor] and I'd prefer keep it like that than doing [String,FileDescriptor] if possible. – Sebastien Lorber Dec 04 '12 at 09:10
Unfortunately, since MongoDB doesn't support using object as the key to a map, what you can do is persist a list of case classes and convert it to a map as a lazy val inside your case class. Requiring the keys to maps to be strings is an explicit limitation of MongoDB. – prasinous Dec 04 '12 at 16:35

Enumerations -> Sealed trait with a "Value"?

1 Answers1