MongoDB

Introduction

NoSQL databases are non-relational databases that are used to store and retrieve data. MongoDB is a popular NoSQL database that is used to store data in the form of documents.

Installation

There are two ways of working with a mongoDB database, one is to run it locally on your machine and the other is to use a cloud service like MongoDB Atlas. For this tutorial, we will be using MongoDB with mongosh and compass installed.

What is mongosh and what is compass?
MongoDB Shell (mongosh) is a shell-centric cross-platform MongoDB shell that provides a rich programming experience for MongoDB. MongoDB Compass is the GUI for MongoDB. It allows you to explore your data, run queries, and interact with your data with full CRUD functionality.

Installation can be found here

• MongoDB - compass included
• MongoDB - mongosh

Basics of MongoDB

MongoDB stores data in the form of documents. A document is a data structure composed of field and value pairs. MongoDB documents are similar to JSON objects. The values of fields may include other documents, arrays, and arrays of documents.

Commands

Basics

• Launching mongo: To launch mongoDB from the terminal, type mongosh and hit enter. This should open a mongo shell provided you have installed it and rebooted your computer.
• Showing databases: To show all the existing databases on the server, type show dbs.
• Creating a database: To create a new database, type use <database_name>. This will create a new database if it doesn’t already exist. If the database already exists, it will switch to that database.
• Clearing screen: Using cls will clear the screen.
• Showing current database: To see the current database you are working on, type db. However it is also reflected in the shell prompt always.
• Exiting: Using exit will exit the mongo shell.
• Collections: Using show collections will show all the collections in the current database.

What are collections and documents?

• Collections: A collection is a group of MongoDB documents. It is the equivalent of an RDBMS table. A collection exists within a single database. Collections do not enforce a schema. Documents within a collection can have different fields. Typically, all documents in a collection are of similar or related purpose.
• Documents: A document is a set of key-value pairs. Documents have dynamic schema. Dynamic schema means that documents in the same collection do not need to have the same set of fields or structure, and common fields in a collection’s documents may hold different types of data.

CRUD Operations

• Create: To insert a document into a collection, use the insertOne() method. For example, db.collection_name.insertOne({field1: value1, field2: value2}).
  • Insert Many: To insert multiple documents into a collection, use the insertMany() method. For example, db.collection_name.insertMany([{field1: value1, field2: value2}, {field1: value3, field2: value4}]).
• Read: To read documents from a collection, use the find() method. For example, db.collection_name.find().
  • Limit: To limit the number of documents returned, use the limit() method. For example, db.collection_name.find().limit(5).
  • Sort: To sort the documents returned, use the sort() method. For example, db.collection_name.find().sort({field1: 1}) (ascending) or db.collection_name.find().sort({field1: -1}) (descending).
• Update: To update a document in a collection, use the updateOne() method. For example, db.collection_name.updateOne({field1: value1}, {$set: {field2: value2}}).
• Delete: To delete a document from a collection, use the deleteOne() method. For example, db.collection_name.deleteOne({field1: value1}).