CODEWITHSUNDEEP
scalainheritancecase-class
jens
jens

Reputation: 453

How to share behavior over case classes in scala

Implementing my domain model in scala using case classes I got

abstract class Entity {
    val _id: Option[BSONObjectID]
    val version: Option[BSONLong]
}

and several case classes defining the different entities like

case class Person (
   _id: Option[BSONObjectID],
   name: String, 
   version: Option[BSONLong]
) extends Entity

What I need is a way to set the _id and version later on from a generic method which operates on an Entity because I have to share this behavior over all Entities and want to avoid writing it down hundreds of times ;-). I would love to be able to

def createID(entity: Entity): Entity = {
  entity.copy(_id = ..., version = ...)
}

...but of course this does not compile since an Entity has no copy-method. It is generated for each single case class by the compiler...

What is the best way to achieve this in scala?

To prevent somebody asking: I have to use case classes since this is what the third-party-library is extracting for me from the requests I get and the case class instances are what is serialized back to BSON / MongoDB later on...

Upvotes: 4

Views: 667

Answers (2)

jens
jens

Reputation: 453

Indeed one can find a way to implement something like this at

Create common trait for all case classes supporting copy(id=newId) method

but since it is quite complicated for my use case I would prefer just to create two new classes

class MongoId(var id : BSONObjectID = null) {
    def generate = {
        id = BSONObjectID.generate
    }
}

class MongoVersion(var version: Long = 0) {
    def update = {
        version = System.currentTimeMillis
    }
}

and implemented the shared behavior regarding these fields there. Of course you have to change the definition of your base class accordingly:

abstract class Entity {
    def _id: MongoId
    def version: MongoVersion
}

To make it clear: This works only if the behavior you want to share over several case classes does only affect (in my case changes) one attribute ...

Upvotes: 3

WestCoastProjects
WestCoastProjects

Reputation: 63062

Would implementing a trait work?

trait MongoIdHandler {
  def createId(entity : Entity) : Option[BSONObjectID] = { ..}
  def setVersion(version :  String) : Unit = { ..}
}

case class Person (..) with MongoIdHandler ..

If any of the instances require specialized versions of the id generator they can override the 'default' impl provided by the trait.

Upvotes: 0

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