Casbah - A Scala library for MongoDB

Introduction

• Casbah integrates a layer on top of the official mongo-java-driver for better integration with Scala

• This is as opposed to a native implementation of the MongoDB wire protocol, which the Java driver does exceptionally well. Rather than a complete rewrite, Casbah uses implicits, and Pimp My Library code to enhance the existing Java code

• Casbah aims to remain fully compatible with the existing Java driver—it does not talk to MongoDB directly, preferring to wrap the Java code

Dependencies

Maven

<dependency>
	<groupId>org.mongodb</groupId>
	<artifactId>casbah-core_2.10</artifactId>
	<version>2.8.1</version>
</dependency>

SBT

libraryDependencies += "org.mongodb" %% "casbah" % "3.1.1"

Using Casbah

• Core lives in the package namespace com.mongodb.casbah

• Casbah uses a few tricks to act as self contained as possible - it provides an Imports object which automatically imports everything you need including Implicit conversions and type aliases to a few common MongoDB types.

• This means you should only need to use our Imports package for the majority of your work

• The Imports call will make common types such as DBObject, MongoConnection and MongoCollection available

• Core‘s Imports also run the imports from Commons and the Query DSL

• The general idea is that common Java types (such as ArrayList) will be returned as the equivalent Scala type.

Connecting to MongoDB

• The core Connection class is com.mongodb.casbah.MongoConnection

• There are two ways to create an instance of it :

  First, you can invoke .asScala from a MongoDB builtin Connection (com.mongodb.Mongo)

  The pure Scala way to do it is to invoke one of the apply methods on the companion object:

  // Connect to default - localhost, 27017 val mongoConn = MongoConnection() val mongoConn = MongoConnection("mongodb01") val mongoConn = MongoConnection("mongodb02", 42001)

  // Using the URI method ( preferable ) val mongouri = MongoClientURI("mongodb://127.0.0.1") val mongoConn = MongoClient(mongouri)

  // Get a collection val collection:MongoCollection = mongoConn("<db_name>")("<collection_name>")

• Casbah’s MongoCollection object implements Scala’s Iterable[A] interface (specifically Iterable[DBObject]), which provides a full monadic interface to your MongoDB collection

• Beginning iteration on the MongoCollection instance is fundamentally equivalent to invoking find on the MongoCollection

MongoDBObject - A Scala-ble DBObject Implementation

• MongoDBObject and its companion trait provide a series of ways to work with Mongo’s DBObjects which closely match the Collection interface Scala 2.8 provides.

• Further, MongoDBObject can be implicitly converted to a DBObject

  • so any existing Mongo Java code will accept it without complain

• There are two easy ways to create a new MongoDBObject

• You could also use a Scala 2.8 style builder to create your object instead:

  val builder = MongoDBObject.newBuilder builder += "foo" -> "bar" builder += "x" -> "y" builder += ("pie" -> 3.14) builder += ("spam" -> "eggs", "mmm" -> "bacon") val newObj = builder.result Being a builder - you must call result to get a DBObject.

Saving data with Casbah

val obj = MongoDBObject("product" -> "Colgate maxfresh","price" -> 60 ,"customer" -> "Nilanjan") collection.save(obj)

Updating data with Casbah

val q = MongoDBObject("product" -> "Colgate maxfresh","price" -> 60 ,"customer" -> "Nilanjan") val latest = MongoDBObject("product" -> "Colgate maxfresh","price" -> 66 ,"customer" -> "Nilanjan") collection.findAndModify(q, mapper.buildMongoDbObject(latest))

Querying with Casbah

val res = collection.find("customer" $eq "Nilanjan")

Deleting with Casbah

val q: MongoDBObject = MongoDBObject("product" -> "Colgate maxfresh","price" -> 60 ,"customer" -> "Nilanjan") collection.findAndRemove(mongoObj)

Important Classes

com.mongodb.casbah.MongoClientURI com.mongodb.casbah.MongoClientOptions com.mongodb.casbah.MongoClient com.mongodb.casbah.MongoCollection

Sources

https://mongodb.github.io/casbah/ http://api.mongodb.com/scala/casbah/2.0/tutorial.htmlS https://alvinalexander.com/search/node?keys=casbah