Chapter 2. Getting Started
MongoDB is very powerful, but it is still 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, roughly equivalent to a row in a relational database management system (but much more expressive).
Similarly, a collection can be thought of as the schema-free equivalent of a table.
A single instance of MongoDB can host multiple independent databases, each of which can have its own collections and permissions.
MongoDB comes with a simple but powerful JavaScript shell, which is useful for the administration of MongoDB instances and data manipulation.
Every document has a special key,
"_id"
, that is unique across the document’s collection.
Documents
At the heart of MongoDB is the concept of a document: an ordered set of keys with associated values. The representation of a document differs 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!", "foo" : 3}
This example is a good illustration of several important concepts:
Key/value pairs in documents are ordered—the earlier document is distinct from ...
Get MongoDB: The Definitive Guide now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.