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.
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