MongoDB Introduction

MongoDB  is an open-source document database, and the leading NoSQL database. Written in C++, with many great features like map-reduce , auto sharding, replication, high availability and etc.

• MongoDB works on concept of collection and document. 

• Stores JSON-style documents with flexible schemas represented as  (BSON -> Binary JSON).

• Built for Speed

• Rich Document based queries for Easy readability. 

• Full Index Support for High Performance.

• Replication and Failover for High Availability.

• Auto Sharding for Easy Scalability. 

• Map / Reduce for Aggregation. 

• MongoDB stores documents (or) objects.

• Embedded documents and arrays reduce need for joins. No Joins and No-multi document transactions.

MongoDB Designs Goals

Terminology and Concepts

The following table presents the various SQL terminology and concepts and the corresponding MongoDB terminology and concepts.

SQL Terms/Concepts	MongoDB Terms/Concepts
database	database
table	collection
row	document or BSON document
column	field
index	index
table joins	embedded documents and linking
primary key Specify any unique column or column combination as primary key.	primary key In MongoDB, the primary key is automatically set to the_id field.
aggregation (e.g. group by)	aggregation pipeline See the SQL to Aggregation Mapping Chart.

The MongoDB examples :

assume a collection named users that contain documents of the following prototype:

1.

{

  _id: ObjectId("509a8fb2f3f4948bd2f983a0"),

  user_id: "abc123",

  age: 55,

  status: 'A'

}

assume a collection named posts that contain documents of the following prototype:

2.

{

‘_id’: ‘3432’,

‘author’: DBRef(‘User’, 2), 

‘title’: ‘Introduction to MongoDB’,

‘body’: ‘MongoDB is an open sources.. ‘,

‘timestamp’: Date(’01-04-12’),

‘tags’: [‘MongoDB’, ‘NoSQL’],

‘comments’: [{‘author’: DBRef(‘User’, 4),

‘date’: Date(’02-04-12’),

‘text’: ‘Did you see.. ‘,

‘upvotes’: 7, … ]

}