What is Sequelize and ORM

• Sequelize is an Object-Relational Mapping (ORM) library for Node.js. It provides a high-level abstraction for dealing with databases, allowing developers to work with JavaScript objects instead of SQL queries. Sequelize supports various dialects, such as PostgreSQL, MySQL, SQLite, and Microsoft SQL Server, enabling developers to write uniform code across different database systems.

The key features of Sequelize include:

• Model Definition: Models are defined with JavaScript objects, mapping between JS code and database tables.

• Schema Migration: Sequelize supports migrations, allowing you to evolve your database schema over time in a version-controlled manner.

• CRUD Operations: It provides easy-to-use methods for creating, reading, updating, and deleting database entries.

• Associations: Sequelize can handle one-to-one, one-to-many, and many-to-many associations.

• Validation and Constraints: You can define validations and constraints directly in your model, ensuring data integrity.

• Transactions: It supports transactions, enabling complex operations to be executed in a safe way.

• Querying: Sequelize offers a powerful querying mechanism that includes support for filtering, sorting, and pagination.

ORM:

• In the context of Sequelize, ORM stands for Object-Relational Mapping. ORM is a programming technique used to convert data between incompatible type systems in object-oriented programming languages.

Here's how it applies to Sequelize, which is an ORM library for Node.js:

• Abstraction Layer: ORM serves as an abstraction layer between the relational database and the application's business model. This means developers can work with database entities using JavaScript objects instead of writing SQL queries directly.

• Data Mapping: It maps JavaScript objects to database tables (and vice versa), allowing for a more intuitive and high-level interaction with the database. Each instance of a model represents a row in the table.

• Database Agnostic: Sequelize, as an ORM, abstracts the specific dialects of various SQL databases (like PostgreSQL, MySQL, SQLite, and SQL Server), enabling developers to switch between databases with minimal changes to the application code.

• CRUD Operations: ORM facilitates Create, Read, Update, and Delete (CRUD) operations on the database through simple and easy-to-use methods. This helps in writing cleaner, more maintainable code.

• Associations/Relations: Sequelize ORM allows the definition of associations between different models (tables) such as one-to-one, one-to-many, and many-to-many relationships, reflecting the relational database principles directly within the application logic.

• Migration and Schema Definition: ORM supports defining database schemas and migrations directly through the application code, allowing for version-controlled evolution of the database schema.

• In summary, in the context of Sequelize, ORM simplifies database interactions by providing a JavaScript-based interface to perform complex SQL operations, manage relationships between data entities, and maintain the database schema, making it more accessible and manageable for developers.