Scala MongoDB Chaining Methods

Question

i'd like to ask for your help about beautifying client code.

Let's say I have some basic methods for MongoDB retrieval:

 def find(dbo:DBObject):MongoCursor =
    mongoColl.find(dbo)

  def Sort(cursor: MongoCursor, sortFun: DBObject): MongoCursor =
    cursor.sort(sortFun)

  def Limit(cursor: MongoCursor, number: Int): MongoCursor = cursor.limit(number)

  def Offset(cursor: MongoCursor, number: Int): MongoCursor = cursor.skip(number)

  def toList(cursor: MongoCursor): List[A] =
   cursor map (readConverter(_)) toList

and i wanna chain them together in different ways (let say i wanna perform some limited searchs, some sorted searchs, just like a decorator basically). how would you do it?

Thanks for your help.

Answer 1

You could try to use an implicit value class to enrich the MongoCursor:

object ImplicitClassContainer {
  implicit class RichMongoCursor(val mc: MongoCursor) extends AnyVal {
    def sort(sortFun: DBObject): MongoCursor = mc.sort(sortFun)

    def limit(number: Int): MongoCursor = mc.limit(number)

    def offset(number: Int): MongoCursor = mc.skip(number)
  }

}

to be used like this

  import ImplicitClassContainer._

  def x(mc: MongoCursor): MongoCursor = {
    mc.offset(25).limit(25)
  }

Basically it's the same pattern which is used to add functionality to Array: You get additional functions in "flow style", but it's still a MongoCursor. As it is an implicit value class, no additional instance of an object is created at run-time.