MongoDB commands to Scala Casbah examples

MongoDBToCasbahExamples.scala

import com.mongodb.casbah.Imports._
import com.mongodb.casbah.commons.MongoDBObject

class MongoDBToCasbahExamples {

  /* The BSON structure that will be used for the examples
  {
    "userId": "134256",
    "currencyFrom": "EUR",
    "currencyTo": "GBP",
    "amountSell": 1000,
    "amountBuy": 747.1,
    "rate": 0.7471,
    "originatingCountry": "FR"
  }
 */

  /* The MongoDB connection */
  private val collection = {
    val connection = MongoClient("some-host", 12345)
    connection("some-database")("some-collection")
  }

  /**
   * Persists a trade object to MongoDB
   *
   * ==Corresponds to the following MongoDB command==
   *
   * db.trades.insert({
   *   "userId": "134256",
   *   "currencyFrom": "EUR",
   *   "currencyTo": "GBP",
   *   "amountSell": 1000,
   *   "amountBuy": 747.1,
   *   "rate": 0.7471,
   *   "originatingCountry": "FR"
   * })
   *
   */
  def persistTrade = {
    // create the MongoDBObject
    val dbObject = {
      val builder1 = MongoDBObject.newBuilder
      builder1 += "userId" -> "lukeskywalker"
      builder1 += "currencyFrom" -> "EUR"
      builder1 += "currencyTo" -> "USD"
      builder1 += "amountSell" -> 1245.67
      builder1 += "amountBuy" -> 978.10
      builder1 += "rate" -> 0.7852
      builder1 += "originatingCountry" -> "AU"
      builder1.result
    }

    // insert the DBObject to MongoDB
    collection.save(dbObject)
  }

  /**
   * Retrieves the top 10 countries by trade volume.
   *
   * ==Corresponds to the following MongoDB query==
   *
   *  db.trades.aggregate( [
   *    { $group : { _id : "$originatingCountry", volume: { $sum: 1 } } },
   *    { "$project":{"_id":0, "country":"$_id", "volume": 1 } },
   *    { $sort: { count: -1 } },
   *    { $limit:10 }
   *  ] )
   *
   * @return List[DBObject] the top 10 countries by trade volume
   */
  def getCountriesByTradeVolume: List[DBObject] = {
    collection.aggregate(
      List(
        // the $group query
        MongoDBObject("$group" -> MongoDBObject(
          "_id" -> "$originatingCountry",
          "volume" -> MongoDBObject("$sum" -> 1)
        )),
        // the $project query
        MongoDBObject("$project" ->
          MongoDBObject("_id" -> 0, "country" -> "$_id", "volume" -> 1)),
        // the $sort query
        MongoDBObject("$sort" -> MongoDBObject("volume" -> -1)),
        // the $limit query
        MongoDBObject("$limit" -> 10)
      ),
      // the aggregation
      AggregationOptions(AggregationOptions.CURSOR)
    ).toList
  }

  /**
   * Retrieves the top 10 currency pairs by volume sold.
   *
   * ==Corresponds to the following MongoDB query==
   *
   *  db.trades.aggregate([
   *    { "$group": { "_id": { "currencyFrom": "$currencyFrom", "currencyTo": "$currencyTo" }, "volume": { "$sum": 1 } }},
   *    { "$project":{"_id":0, "currencyPair":"$_id.currencyFrom", "currencyTo":"$_id.currencyTo", "volume": 1 } },
   *    { $sort: { volume: -1 } },
   *    { $limit:10 }
   *  ])
   *
   * @return List[DBObject] the top 10 currency pairs by volume sold
   */
  def getCurrencyPairsByVolume: List[DBObject] = {
    collection.aggregate(
      List(
        // the $group query
        MongoDBObject("$group" -> MongoDBObject(
          // definition of composite _id
          "_id" -> MongoDBObject("currencyFrom" -> "$currencyFrom", "currencyTo" -> "$currencyTo"),
          "volume" -> MongoDBObject("$sum" -> 1)
        )),
        // the $project query
        MongoDBObject("$project" ->
          MongoDBObject("_id" -> 0, "currencyFrom" -> "$_id.currencyFrom", "currencyTo" -> "$_id.currencyTo", "volume" -> 1)),
        // the $sort query
        MongoDBObject("$sort" -> MongoDBObject("volume" -> -1)),
        // the $limit query
        MongoDBObject("$limit" -> 10)
      ),
      // the aggregation
      AggregationOptions(AggregationOptions.CURSOR)
    ).toList
  }

  /**
   * Finds the latest 10 trades
   *
   * ==Corresponds to the following MongoDB query==
   *
   *  db.trades.find(
   *    null,
   *    {_id:0, currencyFrom:1, currencyTo:1, amountSell:1, amountBuy:1, rate:1, originatingCountry:1 }
   *  )
   *  .sort( {originatingCountry:-1} )
   *  .limit(10)
   *
   * @return List[DBObject] the latest 10 trades
   */
  def getLatestTrades: List[DBObject] = {
    collection.find(
      // equivalent to a null entry in a MongoDB command
      MongoDBObject.empty,
      // the list of fields to display from the retrieved objects
      MongoDBObject(
        "_id" -> 0,
        "currencyFrom" -> 1,
        "currencyTo" -> 1,
        "amountSell" -> 1,
        "amountBuy" -> 1,
        "rate" -> 1,
        "originatingCountry" -> 1
      )
    )
      // the sort query
      .sort(MongoDBObject("originatingCountry" -> -1))
      // the limit query
      .limit(10)
      .toList
  }

  /**
   * Retrieves the distinct countries from which a trade has been placed.
   *
   * ==Corresponds to the following MongoDB query==
   *
   *  db.trades.distinct("originatingCountry")
   *
   * @return List[String] the countries codes
   */
  def getCountryCodes: List[String] = {
    collection.distinct("originatingCountry").map(e => e.toString).sortWith(_ < _).toList
  }

}