Sequelize
By the Sequelize open-source community
js that provides model definitions, associations, transactions, and migrations for relational databases.
Definition
Sequelize is a promise-based Object-Relational Mapping (ORM) library for Node.js that provides model definitions, associations, transactions, and migrations for relational databases.
Overview
Sequelize was one of the earliest widely adopted ORMs in the Node.js ecosystem, predating TypeScript's mainstream popularity, so its core API is JavaScript-first: models are defined by calling `sequelize.define()` or extending a `Model` class with a plain configuration object describing columns, types, and validations. It supports PostgreSQL, MySQL, MariaDB, SQLite, and Microsoft SQL Server through a common dialect-abstracted API, and handles associations (one-to-many, many-to-many, polymorphic) with helper methods generated automatically on each model. Schema evolution is handled by Sequelize's own CLI, `sequelize-cli`, which scaffolds migration files similar in spirit to Flyway or Liquibase but written as JavaScript `up`/`down` functions rather than SQL or XML. This gives migrations the same procedural flexibility as Alembic's Python scripts, at the cost of needing discipline to keep them idempotent and safe to rerun. Sequelize includes a query interface for raw SQL when the ORM's abstractions become limiting, along with built-in support for transactions, hooks (lifecycle callbacks like `beforeCreate`), and eager/lazy loading of associations. It remains popular in Express.js applications, though newer, more strongly typed alternatives such as TypeORM, Prisma, and Drizzle ORM have captured much of the TypeScript-first segment of the ecosystem in recent years. For teams building REST or GraphQL APIs on Node.js, Sequelize remains a mature, battle-tested option with a large plugin and middleware ecosystem, and it is commonly covered alongside courses like Node.js & Express.
Key Features
- JavaScript-first model definitions with column types and validations
- Automatic association methods for one-to-many and many-to-many relations
- Promise-based API with async/await support throughout
- sequelize-cli for scaffolding and running versioned migrations
- Lifecycle hooks (beforeCreate, afterUpdate, etc.) for custom logic
- Transaction support, including managed and unmanaged transactions
- Multi-dialect support for PostgreSQL, MySQL, MariaDB, SQLite, and SQL Server
- Raw query interface for cases the ORM abstraction doesn't cover well