Understanding MongoDB

MongoDB is a NoSQL-based distributed document data storage. This has been specially designed for providing scalable and high performance data storage solutions. In many scenarios, it can be used to replace traditional relational database or key/value data storage. The biggest feature of Mongo is its query language, which is very powerful, and its syntax is somewhat similar to object-oriented query language.

The following are the features of MongoDB:

  • Set-oriented storage and easy to store the object type
  • Support for dynamic queries
  • Full index support
  • Rich query language
  • Data fragments processing order to support the expansion of the cloud level
  • BSON-based file data storage
  • Supported with C, C++, C#, Erlang, Haskell, Java, JavaScript, Perl, PHP, Python, Ruby, and Scala

We can use R and MongoDB together by installing the following prerequisites:

  • MongoDB installation
  • rmongodb installation

Installing MongoDB

The following are the steps provided for installation of MongoDB in Ubuntu 12.04 and CentOS:

First, we will see installation steps for Ubuntu.

  1. Configure Package Management System (APT) using the following command:
    sudo apt-key adv --keyserverhkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
  2. Create /etc/apt/sources.list.d/mongodb.list by using the following command:
    echo 'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen' | sudo tee /etc/apt/sources.list.d/mongodb.list
  3. Now, update the package list of your OS using the following command:
    sudo apt-get update
  4. Install the latest version of MongoDB by using the following command:
    apt-get install mongodb-10gen

Now, we will see the installation steps for CentOs.

  1. Configure Package Management System (YUM).
  2. Create /etc/yum.repos.d/mongodb.repo and use the following configurations:
    • For a 64-bit system use the following command:
      [mongodb]
name=MongoDB Repository
baseurl=http://downloads-distro.mongodb.org/repo/redhat/os/x86_64/
gpgcheck=0
enabled=1
    • For a 32-bit system use the following command:
      [mongodb]
name=MongoDB Repository
baseurl=http://downloads-distro.mongodb.org/repo/redhat/os/i686/
gpgcheck=0
enabled=1
  3. Install Packages.

With the following command, install a stable version of MongoDB and the associated tools:

yum install mongo-10gen mongo-10gen-server

Now, you have successfully installed MongoDB.

Tip

Useful commands for controlling a mongodb service

To start the mongodb service we use the following command:

sudo service mongodb start

To stop the mongodb service we use the following command:

sudo service mongodb stop

To restart the mongodb service we use the following command:

sudo service mongodb restart

To start a Mongo console we use the following command:

mongo

Mapping SQL to MongoDB

The following are the mappings of SQL terms to MongoDB terms for better understanding of data storage:

No.

SQL Term

MongoDB Term

1.

Database

Database

2.

Table

Collection

3.

Index

Index

4.

Row

Document

5.

Column

Field

6.

Joining

Embedding & linking

Mapping SQL to MongoQL

The following are the mapping of SQL statements to Mongo QL statements for the understanding of query development/conversion:

No.

SQL Statement

Mongo QL Statement

1.

INSERT INTO students VALUES(1,1)

$db->students->insert(array("a" => 1, "b" => 1));

2.

SELECT a, b FROM students

$db->students->find(array(), array("a" => 1, "b" => 1));

3.

SELECT * FROM students WHERE age < 15

$db->students->find(array("age" => array('$lt' => 15)));

4.

UPDATE students SET a=1 WHERE b='q'

$db->students->update(array("b" => "q"), array('$set' => array("a" => 1)));

5.

DELETE FROM students WHERE name="siddharth"

$db->students->remove(array("name" => " siddharth"));

Installing rmongodb

To use MongoDB within R, we need to have installed R with the rmongodb library. We can install rmongodb from CRAN via the following command:

# installing library rmongodb in R
install.packages (rmongodb)

Importing the data into R

We have learned how to install MongoDB in Ubuntu 12.04. Now, we can perform all the necessary operations on our data. In this section, we are going to learn how Mongo data can be handled and imported in R for data analytics activity. For loading the library we use the following command:

# loading the library of rmongodb
library (rmongodb)

Mongo connection establishment
mongo <-mongo.create ()

Check whether the normal series
mongo.is.connected (mongo)

Create a BSON object cache
buf <- mongo.bson.buffer.create ()

Add element to the object buf
mongo.bson.buffer.append (buf, "name", "Echo")

Objects of the mongo.bson class are used to store BSON documents. BSON is the form that MongoDB uses to store documents in its database. MongoDB network traffic also uses BSON messages:

b <- mongo.bson.from.list(list(name="Fred", age=29, city="Boston"))iter <- mongo.bson.iterator.create(b)  # b is of class "mongo.bson"while (mongo.bson.iterator.next(iter))print(mongo.bson.iterator.value(iter))

Understanding data manipulation

We will now see how Mongo data object can be operated within R:

# To check whether mongo is connected or not in R.
if (mongo.is.connected(mongo)) {ns <- "test.people"
#Returns a fresh mongo.bson.buffer object ready to have data 
#appended onto it in R.buf <- mongo.bson.buffer.create()mongo.bson.buffer.append(buf, "name", "Joe")criteria <- mongo.bson.from.buffer(buf)

# mongo.bson.buffer objects are used to build mongo.bson objects.buf <- mongo.bson.buffer.create()
  mongo.bson.buffer.start.object(buf, "inc")mongo.bson.buffer.append(buf, "age", 1L)mongo.bson.buffer.finish.object(buf)objNew <- mongo.bson.from.buffer(buf)# increment the age field of the first record   matching name "Joe"mongo.update(mongo, ns, criteria, objNew)

# mongo.bson.buffer objects are used to build mongo.bson objects.buf <- mongo.bson.buffer.create()mongo.bson.buffer.append(buf, "name", "Jeff")criteria <- mongo.bson.from.buffer(buf)

# mongo.bson.buffer objects are used to build mongo.bson objects.buf <- mongo.bson.buffer.create()mongo.bson.buffer.append(buf, "name", "Jeff")mongo.bson.buffer.append(buf, "age", 27L)objNew <- mongo.bson.from.buffer(buf)# update the entire record to { name: "Jeff", age: 27 }# where name equals "Jeff"# if such a record exists; otherwise, insert this as a new reordmongo.update(mongo, ns, criteria, objNew,mongo.update.upsert)# do a shorthand update:mongo.update(mongo, ns, list(name="John"), list(name="John", age=25))}
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