Querying CouchDB views with Sprouch

In this tutorial you will learn how to query CouchDB views with Sprouch. I will assume that you already know how views work and how to write Javascript views. I will also assume that you have read the basic Sprouch tutorial and know how to connect to CouchDB with Sprouch. You will need the usual imports to get started. You can view the source code of this tutorial at its github repository.

object ViewsTutorial extends App with Helpers {
  import sprouch._, dsl._, JsonProtocol._
  import akka.dispatch.{Await, Future}, akka.util.Duration

First you will need some test data to run your views on. The following creates a sequence of ShopItems with prices between 100 and 1000.

  val items = for (i <- 1 to 10)
    yield ShopItem("Item " + i, BigDecimal(i * 100), None)

Since creating a database was already covered, I'll assume that you have some function that passes a Future[Database] to its argument. You make the argument implicit to be able to use it with the DSL syntax.

  withDb(implicit dbf => for {

First you create the ShopItem documents in the database.

    docs <- items.create

Then you write the views. The first one just returns the price of the item as the key.

    mapView = MapReduce(
        map = """
          function(doc) {
            emit(doc.price);
          }
        """
    )

The second view computes the sum of all prices.

    reduceView = MapReduce(
        map = """
          function(doc) {
            emit(doc.name, doc.price);
          }
        """,
        reduce = """
          function(keys, values) {
            return sum(values);
          }
        """
    )

You can create the views in the database with the createViews method.

    viewsDoc <- NewDocument(
        "my views",
        Views(Map("price" -> mapView, "sum" -> reduceView))
    ).createViews

Now you can query the map view. This query will get us all items whose price is between 350 and 550. The second type parameter is Null, since the view does not emit values.

    prices <- queryView[Double, Null]("my views", "price",
        flags = ViewQueryFlag(reduce = false, include_docs = true),
        startKey = Some(350),
        endKey = Some(550))
    _ = {
      println("Items between 350 and 550:")
      prices.rows.foreach(r => {
        println(r.docAs[ShopItem].get.name + ": " + r.key)
      })
    }

Querying the reduce view is even simpler. The first type parameter is Null, since the key of this reduce view will be null as it is not grouped.

    sum <- queryView[Null, Double]("my views", "sum")
    _ = println("Sum of prices of all items: " + sum.values.head)
    
  } yield ())
}

That's it! The output will be

Items between 350 and 550:
Item 4: 400.0
Item 5: 500.0
Sum of prices of all items: 5500.0

 

There are many more options for querying views. Sprouch covers CouchDb's complete view API. You can find more information about views in the CouchDb documentation. If you have a question about Sprouch, please leave a comment.