sequelize

What is sequelize?

Sequelize is a promise-based Node.js ORM (Object-Relational Mapping) library for Postgres, MySQL, MariaDB, SQLite, and Microsoft SQL Server. It features solid transaction support, relations, eager and lazy loading, read replication and more. Sequelize follows the Active Record paradigm and allows developers to define models and their relationships in a way that abstracts database access, making it easier to maintain and evolve the application codebase.

What are sequelize's main functionalities?

Model Definition

This feature allows you to define models in Sequelize, which represent tables in the database. Each model can have various attributes and their respective data types.

const User = sequelize.define('user', { username: Sequelize.STRING, birthday: Sequelize.DATE });

CRUD Operations

Sequelize provides methods for creating, reading, updating, and deleting records in the database, which correspond to the CRUD operations.

User.create({ username: 'alice', birthday: new Date(1986, 6, 20) }); User.findAll(); User.update({ username: 'alicejr' }, { where: { id: 1 } }); User.destroy({ where: { id: 1 } });

Associations

This feature allows you to define associations between models. For example, a user can have many posts, and a post belongs to a user.

User.hasMany(Post); Post.belongsTo(User);

Transactions

Sequelize supports transactions which allow you to execute multiple queries in an atomic way, ensuring data integrity.

sequelize.transaction(transaction => { return User.create({ username: 'bob' }, { transaction }); });

Migrations

Sequelize has a migration tool that allows you to define changes to the database schema, which can be applied and rolled back programmatically.

module.exports = { up: (queryInterface, Sequelize) => { return queryInterface.createTable('users', { id: { allowNull: false, autoIncrement: true, primaryKey: true, type: Sequelize.INTEGER }, username: { type: Sequelize.STRING } }); }, down: (queryInterface, Sequelize) => { return queryInterface.dropTable('users'); } };

Other packages similar to sequelize

mongoose

Mongoose is an ODM (Object Data Modeling) library for MongoDB and Node.js. It manages relationships between data, provides schema validation, and is used to translate between objects in code and the representation of those objects in MongoDB. Compared to Sequelize, Mongoose is specific to MongoDB, whereas Sequelize supports multiple SQL databases.

typeorm

TypeORM is an ORM that can run in Node.js and be used with TypeScript and JavaScript (ES5, ES6, ES7, ES8). It supports the Data Mapper pattern, unlike Sequelize which is more Active Record. TypeORM is highly influenced by other ORMs, such as Hibernate, Doctrine, and Entity Framework.

knex

Knex.js is a SQL query builder for Postgres, MSSQL, MySQL, MariaDB, SQLite3, Oracle, and Amazon Redshift, designed to be flexible, portable, and fun to use. It does not provide full ORM capabilities but allows you to build and run SQL queries in a more programmatic and database-agnostic way. It is often used with objection.js, which is an ORM built on top of Knex.

bookshelf

Bookshelf.js is a JavaScript ORM for Node.js, built on the Knex SQL query builder. It features transaction support, eager/nested-eager relation loading, and polymorphic associations. Bookshelf follows a somewhat similar pattern to Sequelize but is built on top of Knex, which gives it a different flavor in terms of query building.

README

Sequelize

The Sequelize library provides easy access to a MySQL database by mapping database entries to objects and vice versa. To put it in a nutshell... it's an ORM (Object-Relational-Mapper). The library is written entirely in JavaScript and can be used in the Node.JS environment.

Features

• Schema definition
• Schema synchronization/dropping
• Easy definition of class/instance methods
• Instance saving/updating/dropping
• Asynchronous library
• Associations
• Importing definitions from single files

Documentation, Examples and Updates

You can find the documentation and announcements of updates on the project's website.
If you want to know about latest development and releases, follow me on Twitter.
Also make sure to take a look at the examples in the repository. The website will contain them soon, as well.

Tests

In order to run the tests, you need the expresso framework! When installed just run:

expresso -s test/**/*