bhudgeons

How to Use the New MongoDB Aggregation Framework Via Scala and Casbah February 22, 2012

Note that this requires MongoDB 2.1+ (at the time of this writing, 2.1 is still the unstable release -- the aggregation framework will be in its first stable release in 2.2).  @rit is adding the aggregation framework to the Casbah DSL, which will make this method superfluous, but it is a good example of how to implement a mongodb command in scala before Casbah or the Java driver support it.

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import com.mongodb.casbah.Imports._

/*
 * Simple test of the MongoDB Aggregation Framework via Casbah
 * 
 * [Note: only works on MongoDB 2.1+]
 * 
 * The "students" collection consists of student test score records that [simplified] look like this:
 * 
   {
	"_id" : ObjectId("4f436e581a8819c9391c9e77"),
	"id" : "1000000321",
	"lname" : "Simpson",
	"fname" : "Bobby",
	"scores" : [
		{
			"score" : 14,
			"dname" : "ACADEMICS PLUS SCHOOL DISTRICT",
			"sname" : "Test School 6040702",
			"tyear" : "2007",
			"tname" : "Lit_Scale",
			"grade" : "3"
		},
		{
			"score" : 557,
			"dname" : "ACADEMICS PLUS SCHOOL DISTRICT",
			"sname" : "Test School 6040702",
			"tyear" : "2007",
			"tname" : "Lit_Perf",
			"grade" : "3"
		},
		{
			"score" : 15,
			"dname" : "ACADEMICS PLUS SCHOOL DISTRICT",
			"sname" : "Test School 6040702",
			"tyear" : "2008",
			"tname" : "Lit_Scale",
			"grade" : "4"
		}
	]
}
 *
 * This example unwinds the scores and groups them
 * to determine the unique values of the tests, years and grades fields.
 * 
 */

object AggregationFrameworkTest extends App {
  val mongoConn = MongoConnection()
  val db = mongoConn("hivedbmig")

  def aggregationResult(collectionName:String, pipeline: MongoDBList) = {
    db.command(MongoDBObject("aggregate" -> collectionName, "pipeline" -> pipeline)).get("result")
  }

  val pipebuilder = MongoDBList.newBuilder
  pipebuilder += MongoDBObject("$unwind" -> "$scores")
  pipebuilder += MongoDBObject("$group" -> MongoDBObject(
      "_id" -> "all", // constant, so we'll just create one bucket
      "tests" -> MongoDBObject("$addToSet" -> "$scores.tname"), 
      "years" -> MongoDBObject("$addToSet" -> "$scores.tyear"), 
      "grades" -> MongoDBObject("$addToSet" -> "$scores.grade")))
      
  val pipeline = pipebuilder.result()
  
  aggregationResult("students", pipeline) match {
    case list: BasicDBList => list.foreach(println(_))
    case _ => println("didn't work")
  }
  // { "_id" : "all" , "tests" : [ "ACT_Comp" , "FPQ4_Score" , "Lit_Growth" , "Math_Scale" , "Bio_Scale" , "Geo_Scale" , "Geo_Growth" , "Math_Growth" , "Alg_Scale" , "ACT_Math" , "ACT_Eng" , "Alg_Growth" , "Sci_Scale" , "Lit_Scale"] , "years" : [ "2011" , "2006" , "2008" , "2009" , "2007" , "2010"] , "grades" : [ "5" , "4" , "7" , "11" , "6" , "3" , "8"]}

}
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