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#5 Collections and Documents in MongoDB

In MongoDB, data is organised into collections and documents.


A collection is a grouping of MongoDB documents. It’s the equivalent of a table in a relational database management system (RDBMS). Collections do not enforce a schema, meaning that documents within a collection can have different fields and structures.


A document is a set of key-value pairs. It’s the basic unit of data in MongoDB, similar to a row in an RDBMS table. Each document in a collection can have a different structure, but they are typically related in some way. Documents are represented in BSON (Binary JSON) format, which is a binary-encoded serialization of JSON-like documents.

mongodb compass example
mongodb compass example

In the above example, we can explore the core elements of MongoDB. On the left panel, we observe the database hierarchy: the overarching entity is the bookstore, while within it lies the collection of books.

  • On the left panel, the bookstore is a database;
  • The books is a collection.
  • In the collection, there are six Documents, each structured in JSON format. These documents contain various fields such as _id, title, author, pages, genres, and rating.
  • Each document within the “books” collection can have different fields or structures. For example, the title is a String, the pages is an Integer and the genres is an Array.