> Mike Valenty

Using Scala to Perform a Multi-Key Get on a Couchbase View

| Comments

To retrieve documents from Couchbase by anything other than the document key requires querying a view and views are defined by map and reduce functions written in JavaScript. Consider a view that returns data like this:

1
2
3
4
5
6

key         value
---         -----
"key1"      { "term": "red", "count": 2 }
"key2"      { "term": "red", "count": 1 }
"key3"      { "term": "blue", "count": 4 }
...

And this Scala case class to hold the documents retrieved from the view.

1

case class TermOccurrence(term: String, count: Int)

It’s a common scenario to retrieve multiple documents at once and the Java driver has a pretty straight forward api for that. The desired keys are simply specified as a json array.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

import com.couchbase.client.CouchbaseClient
import play.api.libs.json.Json
import CouchbaseExtensions._

@Log
def findByTerms(terms: List[String]): List[TermOccurrence] = {

  val keys = Json.stringify(Json.toJson(terms map (_.toLowerCase)))

  val view = client.getView("view1", "by_term")
  val query = new Query()
  query.setIncludeDocs(false)
  query.setKeys(keys)

  val response = client.query(view, query).asScala

  response.toList map (_.as[TermOccurrence])
}

The Java driver deals with strings so it’s up to the client application to handle the json parsing. That was an excellent design decision and makes using the Java driver from Scala pretty painless. I’m using the Play Framework json libraries and an extension method _.as[TermOccurrence] defined on ViewRow to simplify the mapping of the response documents to Scala objects.

1
2
3
4
5
6
7
8
9
10
11

object CouchbaseExtensions {

  implicit class RichViewRow(row: ViewRow) {
    def as[A](implicit format: Format[A]): A = {
      val document = row.getValue
      val modelJsValue = Json.parse(document)
      Json.fromJson[A](modelJsValue).get
    }
  }

}

In order for this extension method to work, it requires an implicit Format[TermOccurrence] which is defined on of the TermOccurrence compainion object.

1
2
3

object TermOccurrence {
  implicit val formatTermOccurrence = Json.format[TermOccurrence]
}

Comments