Lift里进行MongoDB的MapReduce

    def countClicks = {
      MongoDB.useCollection(shortenedUrl.collectionName) {
        x => {
          val map = """function() { emit("totalClickCount", this.%s); }""" format ShortenedUrl.clickCount.name
          val reduce = """function(key, values) { return Array.sum(values); }"""
          val results = x.mapReduce(map, reduce, null, null).results
 
          /**
           * all numbers returned by mongodb is Double since this is how number defined by javascript
           */
          if (results.hasNext) results.next.get("value").asInstanceOf[Number].intValue.toString else "0"
        }
      }
    }