MongoDB Introduction

MongoDB is a document database: it stores each record as a flexible, JSON-like document.

What is MongoDB?

• MongoDB is a NoSQL database, which means it does not use tables and SQL
• Data is stored as documents, which look like JSON objects
• Documents are grouped into collections, and collections into databases
• It is free to use (Community Edition), and MongoDB Atlas is its cloud service with a free tier
• Its name comes from "humongous", because it was built to handle very large amounts of data

What is a Document?

A document is a set of field: value pairs, like a JavaScript object:

{
  _id: ObjectId('6710a1f2c3b4d5e6f7a8b901'),
  name: "Ali Khan",
  city: "Karachi",
  age: 19,
  marks: 78,
  course: "Web Development",
  skills: ["HTML", "CSS"],
  contact: { phone: "0300-1112233", email: "ali@example.com" }
}

• Values can be text, numbers, true/false, dates, arrays (lists) and even other documents (embedded documents), like contact
• Every document has a unique _id. If you do not give one, MongoDB creates an ObjectId for you

MongoDB stores documents in a binary form of JSON called BSON, which adds extra types such as dates and exact decimals.

SQL Words and MongoDB Words

Flexible Schema

In a SQL table, every row has the same columns. In MongoDB, documents in one collection can have different fields:

{ name: "Hamza Raza", city: "Karachi", age: 18, marks: 70 }
{ name: "Fatima Noor", city: "Islamabad", age: 20, marks: 92,
  course: "Graphic Designing", skills: ["Photoshop", "Illustrator"] }

Hamza has not chosen a course yet, so his document simply has no course field.

The Sample Collection

This tutorial uses an institute database with a students collection of six documents:

The table is just for reading; in MongoDB each row is a document like the ones above. You will insert them in the insert lesson.

When to Use MongoDB

Both kinds are used widely, and many companies use both.

Exercise