The officially supported Scala driver for Mongo is Casbah. Cashbah is a thin wrapper around the Java MongoDB driver that gives it a Scala like feel. As long as you ignore all the MongoDBObjects then it feels much more like being in the Mongo shell or working in Python that working with Java/Mongo.

All the examples are copied from a Scala REPL launched from an SBT project with Casbah added as a dependency.

So lets get started by importing the Casbah package:

scala> import com.mongodb.casbah.Imports._ 
import com.mongodb.casbah.Imports._

Now lets create a connection to a locally running Mongo and use the "test" database:

scala> val mongoClient = MongoClient()
mongoClient: com.mongodb.casbah.MongoClient = com.mongodb.casbah.MongoClient@2acf0276
scala> val database = mongoClient("test")
database: com.mongodb.casbah.MongoDB = test

And now lets get a reference to the messages collections:

scala> val collection = database("messages")
collection: com.mongodb.casbah.MongoCollection = messages

As you can see Casbah makes heavy use of the apply method to give relatively nice boiler plate connection code. To print all the rows for a collection you can use the find method which returns an iterator (there is none at the moment):

scala> collection.find().foreach(row => println(row) )

Now lets insert some data the using the insert method and then find and print it:

scala> collection.insert(MongoDBObject("message" -> "Hello world"))
res2: com.mongodb.casbah.Imports.WriteResult = { "serverUsed" : "/127.0.0.1:27017" , "n" : 0 , "connectionId" : 225 , "err" :  null  , "ok" : 1.0}

scala> collection.find().foreach(row => println(row) )
{ "_id" : { "$oid" : "523aa69a30048ee48f49c333"} , "message" : "Hello world"}

And adding another document:

scala> collection.insert(MongoDBObject("message" -> "Hello London"))
res4: com.mongodb.casbah.Imports.WriteResult = { "serverUsed" : "/127.0.0.1:27017" , "n" : 0 , "connectionId" : 225 , "err" :  null  , "ok" : 1.0}

scala> collection.find().foreach(row => println(row) )
{ "_id" : { "$oid" : "523aa69a30048ee48f49c333"} , "message" : "Hello world"}
{ "_id" : { "$oid" : "523aa6bf30048ee48f49c334"} , "message" : "Hello London"}

The familiar findone method is there. Rather than an Iterable object returned from find, findOne returns an Option so you can use a basic pattern match to handle the document being there or not:

scala> val singleResult = collection.findOne()
singleResult: Option[collection.T] = Some({ "_id" : { "$oid" : "523aa69a30048ee48f49c333"} , "message" : "Hello world"})

scala> singleResult match {
     |   case None => println("No messages found")
     |   case Some(message) => println(message)
     | }
{ "_id" : { "$oid" : "523aa69a30048ee48f49c333"} , "message" : "Hello world"}

Now lets query using the ID of an object we've inserted (querying by any other field is the same):

scala> val query = MongoDBObject("_id" -> helloWorld.get("_id"))
id: com.mongodb.casbah.commons.Imports.DBObject = { "_id" : { "$oid" : "523aa69a30048ee48f49c333"}}

scala> collection.findOne(query)
res12: Option[collection.T] = Some({ "_id" : { "$oid" : "523aa69a30048ee48f49c333"} , "message" : "Hello world"})

We can also update the document in the database and then get it again to prove it has changed:

scala> collection.update(query, MongoDBObject("message" -> "Hello Planet"))
res13: com.mongodb.WriteResult = { "serverUsed" : "/127.0.0.1:27017" , "updatedExisting" : true , "n" : 1 , "connectionId" : 225 , "err" :  null  , "ok" : 1.0}

scala> collection.findOne(query)
res14: Option[collection.T] = Some({ "_id" : { "$oid" : "523aa69a30048ee48f49c333"} , "message" : "Hello Planet"})

The remove method works in the same way, just pass in a MongoDBObject for the selection criterion.

Not look Scalary enough for you? You can also insert using the += method:

scala> collection += MongoDBObject("message"->"Hello England")
res15: com.mongodb.WriteResult = { "serverUsed" : "/127.0.0.1:27017" , "n" : 0 , "connectionId" : 225 , "err" :  null  , "ok" : 1.0}

scala> collection.find().foreach(row => println(row))
{ "_id" : { "$oid" : "523aa69a30048ee48f49c333"} , "message" : "Hello Planet"}
{ "_id" : { "$oid" : "523aa6bf30048ee48f49c334"} , "message" : "Hello London"}
{ "_id" : { "$oid" : "523c911230048ee48f49c335"} , "message" : "Hello England"}

How do you build more complex document in Scala? Simply use the MongoDBObject ++ method, for example we can create an object with multiple fields, insert it, then view it by printing all the documents in the collection:

scala> val moreThanOneField = MongoDBObject("message" -> "I'm coming") ++ ("time" -> "today") ++ ("Name" -> "Chris")
moreThanOneField: com.mongodb.casbah.commons.Imports.DBObject = { "message" : "I'm coming" , "time" : "today" , "Name" : "Chris"}

scala> collection.insert(moreThanOneField)
res6: com.mongodb.casbah.Imports.WriteResult = { "serverUsed" : "/127.0.0.1:27017" , "n" : 0 , "connectionId" : 234 , "err" :  null  , "ok" : 1.0}

scala> collection.find().foreach(println(_) )
{ "_id" : { "$oid" : "523aa69a30048ee48f49c333"} , "message" : "Hello Planet"}
{ "_id" : { "$oid" : "523aa6bf30048ee48f49c334"} , "message" : "Hello London"}
{ "_id" : { "$oid" : "523c911230048ee48f49c335"} , "message" : "Hello England"}
{ "_id" : { "$oid" : "523c96b530041dae32fd04d6"} , "message" : "I'm coming" , "time" : "today" , "Name" : "Chris"}