Sequelize Introduction

Introduction
Sequelize is a popular ORM (Object-Relational Mapping) library for Node.js that allows developers to interact with relational databases like MySQL, PostgreSQL, SQLite, and MSSQL using JavaScript. It abstracts the complexities of SQL queries and provides a higher-level interface to work with database tables, records, and relationships.
Key Features of Sequelize -

i) Model Definition

Sequelize allows you to define models that map to tables in your database. Each model represents a table, and each model instance corresponds to a row in that table.

Models are defined using JavaScript classes, making it easy to work with in a Node.js environment.

ii) Querying

Sequelize provides a powerful querying API to perform CRUD (Create, Read, Update, Delete) operations. You can write queries in a more expressive and chainable way rather than using raw SQL.

iii) Associations

Sequelize supports defining relationships between models, such as one-to-one, one-to-many, and many-to-many. This allows you to easily manage related data across different tables.

iv) Migrations

Sequelize comes with a migration tool that helps you manage database schema changes over time. Migrations allow you to apply and rollback changes to your database schema in a controlled way.

v) Validation & Hooks

Sequelize supports data validation, where you can define rules for model attributes, ensuring data integrity. It also provides hooks (or lifecycle events) that allow you to execute custom logic at various stages of model operations, such as before saving or after deleting a record.

vi) Transactions

Sequelize supports database transactions, allowing you to perform multiple operations as a single unit of work. If any operation in the transaction fails, Sequelize can roll back all operations to maintain data consistency.
Why Use Sequelize -

i) Abstraction
Sequelize abstracts the complexities of SQL, making database interactions more intuitive and less error-prone.

ii) Productivity
It speeds up development by allowing you to work with database models as JavaScript objects.

iii) Portability
By supporting multiple dialects (like MySQL, PostgreSQL, etc.), Sequelize makes it easier to switch databases with minimal code changes.

iv) Community
Sequelize has a large community and is well-maintained, meaning you can find plenty of resources and support.
Installation
Make sure you have Node.js and npm (Node Package Manager) installed on your machine. You can check by running,
```
 node -v
 npm -v
```
If you don't already have a package.json file, initialize npm,
```
 npm init -y
```
You can install Sequelize via npm using the following command,
```
 npm install sequelize
```
Sequelize supports different databases, so you'll need to install the appropriate driver for your database,
```
 # PostGres
 npm install pg pg-hstore
 # MySQL
 npm install mysql2
 # SQLite
 npm install sqlite3
 # SQL
 npm install tedious
```
After installing, you can verify that Sequelize is installed by running
```
 npx sequelize --version
```
You should see the version of Sequelize if everything is set up correctly.