MongoDB: The Definitive Guide, 3rd Edition

Chapter 2. Getting Started

MongoDB is powerful but easy to get started with. In this chapter we’ll introduce some of the basic concepts of MongoDB:

• A document is the basic unit of data for MongoDB and is roughly equivalent to a row in a relational database management system (but much more expressive).

• Similarly, a collection can be thought of as a table with a dynamic schema.

• A single instance of MongoDB can host multiple independent databases, each of which contains its own collections.

• Every document has a special key, "_id", that is unique within a collection.

• MongoDB is distributed with a simple but powerful tool called the mongo shell. The mongo shell provides built-in support for administering MongoDB instances and manipulating data using the MongoDB query language. It is also a fully functional JavaScript interpreter that enables users to create and load their own scripts for a variety of purposes.

Documents

At the heart of MongoDB is the document: an ordered set of keys with associated values. The representation of a document varies by programming language, but most languages have a data structure that is a natural fit, such as a map, hash, or dictionary. In JavaScript, for example, documents are represented as objects:

{"greeting" : "Hello, world!"}

This simple document contains a single key, "greeting", with a value of "Hello, world!". Most documents will be more complex than this simple one and often will contain multiple key/value pairs:

{"greeting" : "Hello, world!", "views" ...