Accessing Couchbase from Scala

26 April 2012

In my recent adventure on exploring both Couchbase and Scala, I noticed that there are not many tutorials out there using both at the same time. We’ll use the couchbase-java driver in its latest version (1.1), because it provides support for views and Couchbase 2.0. Note that I won’t cover installing Couchbase here, since there is plenty of material out there. Also, I assume you have scala and sbt already installed. The typesafe stack provides a convenient shortcut to get you up and running in minutes, so check it out if you haven’t already. For the purpos of simplicity, I assume that your Couchbase instance runs on localhost. If it runs elswhere, just modify the URI string later accordingly.

Let’s create the standard directory structure for our project. We’ll use sbt to manage our dependencies, so create a build.sbt file too.

/couchbase-scala
    /src
        /main
            /scala
                Main.scala
    build.sbt

Let’s write the build.sbt first:

name := "couchbase-scala"

version := "1.0"

scalaVersion := "2.9.2"

resolvers += "Couchbase Maven Repository" at "http://files.couchbase.com/maven2"

libraryDependencies += "couchbase" % "couchbase-client" % "1.1-dp"

We need to add the Couchbase Maven Repository to our resolvers list, since it contains the Couchbase package and all its dependencies. The last line adds the actual dependency. If you want the (older) stable release, use “1.0.2” instead of “1.1-dp”. Tip: you can browse the repository directly in your browser and see what versions are available.

Let’s add a simple Main object in Main.scala:

object Main extends App {
    println("Hello World")
}

Now, start sbt and run the application for the first time:

couchbase-scala$ sbt
> run
** ((Omitting Fetch and Compile Output)) **
[info] Running Main
Hello World
[success] Total time: 4 s, completed 24.04.2012 11:01:33

I’ve omited the part where sbt resolves our dependencies and compiles the libraries, but the output should look like the one above. Now that we have all our dependencies in place, we can start talking to the Couchbase server. Here’s a short example with synchronous set and get operations (note that no exception handling takes place here):

import collection.JavaConversions._ 
import collection.mutable.ArrayBuffer

import java.net.URI;
import java.net.ConnectException;

import com.couchbase.client.CouchbaseClient;

object Main extends App {
    val uris = ArrayBuffer(URI.create("http://127.0.0.1:8091/pools"))
    val client = new CouchbaseClient(uris, "default", "")
	
    client.set("hello", 0, "world")
    println("Receiving -> " + client.get("hello"))
	
    client.shutdown()
    System.exit(0)
}

Save the file, type run again in sbt and you should get the following output (you only need to leave the REPL if you’ve changed the build.sbt file):

[info] Compiling 1 Scala source to <Path\to\Sourcecode>\couchbase-scala\target\scala-2.9.2\classes...
[info] Running Main
2012-04-24 11:05:11.850 INFO com.couchbase.client.CouchbaseConnection:  Added {QA sa=/127.0.0.1:11210, #Rops=0, #Wops=0, #iq=0, topRop=null, topWop=null, toWrite=0, interested=0} to connect queue
2012-04-24 11:05:11.856 INFO com.couchbase.client.CouchbaseClient:  viewmode property isn't defined. Setting viewmode to production mode
2012-04-24 11:05:11.856 INFO com.couchbase.client.CouchbaseConnection:  Connection state changed for sun.nio.ch.SelectionKeyImpl@10319d7
2012-04-24 11:05:11.926 INFO com.couchbase.client.ViewConnection:  Added daschl-notebook/127.0.0.1:8092 to connect queue
Receiving -> world
2012-04-24 11:05:12.360 INFO com.couchbase.client.CouchbaseConnection:  Shut down Couchbase client
2012-04-24 11:05:12.368 INFO com.couchbase.client.ViewConnection:  Shut down Couchbase client
2012-04-24 11:05:12.374 INFO com.couchbase.client.ViewNode:  Couchbase I/O reactor terminated
[success] Total time: 6 s, completed 24.04.2012 11:05:12

You see all the Couchbase log messages here, because the default logger logs directly to STDOUT. Right in the middle you can see the output of our synchronous get operation. You should also see the created document in your Couchbase default bucket.

Let’s go through the main code line by line and see what’s going on.

val uris = ArrayBuffer(URI.create("http://127.0.0.1:8091/pools"))	
val client = new CouchbaseClient(uris, "default", "")

The CouchbaseClient accepts a list of URIs to communicate with as the first argument (you need to import collection.JavaConversions._ , so that ÀrrayBuffer gets converted to a java.util.List). The second argument is the bucket name, the third one is an optional bucket password (which is always empty for the default one).

client.set("hello", 0, "world")
println("Receiving -> " + client.get("hello"))

We can now throw all commands at the client, be it synchronous or asynchronous ones. You can find all supported methods here.

client.shutdown()

Finally, we close the connection to the server. You can pass optional timeouts here, so that the client waits for the given amount of time before it finally closes the connection. This allows asynchronous commands to finish first.

This post was a very basic introduction on using Couchbase from Scala. The next post will translate the tutorial to Scala. As always, I’m open to suggestions and improvements!

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