sequelize/sequelize

Sequelize is an ORM (Object-Relational Mapper) for Node.js, a library that lets JavaScript and TypeScript developers interact with a relational database by writing regular code objects and methods instead of writing SQL queries by hand. Rather than constructing a string like "SELECT * FROM users WHERE id = 5", a developer using Sequelize writes something closer to "User.findByPk(5)" and the library translates that into the appropriate SQL and returns the result as a JavaScript object. The library handles the translation layer between the application's data structures and the database tables, including defining models (representations of database tables as code), setting up relationships between tables (such as a user having many posts), and performing queries with filtering, sorting, and pagination. It also manages database transactions, a way of grouping multiple database operations so they either all succeed or all fail together, preventing partial updates that leave data in an inconsistent state. It supports eager loading (fetching related records in one query) and lazy loading (fetching them later on demand). Sequelize supports multiple database systems including PostgreSQL, MySQL, MariaDB, SQLite, Microsoft SQL Server, Oracle DB, Snowflake, DB2, and DB2 for IBM i, which means a developer can switch databases with minimal code changes. A Node.js developer building a web application with a relational database would use Sequelize to avoid writing repetitive SQL, to keep database logic organized as reusable models in code, and to make the codebase easier to maintain. It is written in TypeScript.