Kysely

Kysely is a type-safe SQL query builder for TypeScript and Node.js. It provides a fluent, composable API for constructing SQL queries with compile-time type safety against a user-defined database schema. By defining a database interface that describes tables and their row shapes, developers receive strongly typed query results and can catch column or join mismatches during development rather than at runtime.

The library is database-agnostic in its API and relies on drivers or dialect adapters to communicate with specific databases. It supports popular SQL engines through drivers, enabling work with PostgreSQL, MySQL, SQLite, and related systems by wiring a corresponding driver to the Kysely instance. The same query construction API remains consistent across dialects, while the underlying driver handles database-specific behavior.

Key features include support for typical SQL statements such as select queries with joins, where clauses, group by and order by, as well as inserts, updates, and deletes. It also provides capabilities for transactions, prepared statements, and raw SQL through a typed interface. Result types are inferred from the defined database schema, helping ensure that code accessing rows uses correct column names and types.

Usage typically involves defining a DB interface that maps table names to their row types, creating a Kysely instance bound to a specific driver, and then composing queries using the type-safe API. Kysely does not include a built-in schema migration system, so developers commonly use external migration tooling alongside the library.