ReactiveMongo aggregation pipeline example

YearOrderIncomeReport.scala

  private def query( ): Future[ List[ JsObject ] ] = {
    val group: Group = Group( BSONString( "$order.year" ) )( ("total", SumField( "value" )) )
    val pipeline: Seq[ PipelineOperator ] = Seq( group )
    val command: Future[ Stream[ BSONDocument ] ] = db.command( Aggregate( "opportunities", pipeline ) )
    command map {
      c =>
        c.toList map {
          d =>
            toJSON( d ).asInstanceOf[ JsObject ]
        }
    }
  }