Knex.js (pronounced /kəˈnɛks/) is a "batteries included" SQL query builder for PostgreSQL, CockroachDB, MSSQL, MySQL, MariaDB, SQLite3, Better-SQLite3, Oracle, and Amazon Redshift designed to be flexible, portable, and fun to use. It features both traditional node style callbacks as well as a promise interface for cleaner async flow control, a stream interface, full-featured query and schema builders, transaction support (with savepoints), connection pooling and standardized responses between different query clients and dialects.

As of Mar 29, 2024, Knex has 1,625,784 weekly downloads on npm (3rd most popular SQL library). It is a very popular query builder for Node.js and TypeScript.

Knex IS legendary, but since it was created before TypeScript blew up, it's type capabilities are nothing to write home about. This why Kysely was created.

Kysely (pronounced “Key-Seh-Lee”) is a type-safe and autocompletion-friendly TypeScript SQL query builder. Inspired by Knex. Mainly developed for Node.js but also runs on Deno and in the browser.

kysely-knex is a toolkit (dialect, type translators, custom migration source, etc.) that allows using your existing Knex setup with Kysely. This'll allow you to gradually migrate your codebase from Knex to Kysely.

Main dependencies:

npm install kysely kysely-knex knex

PostgreSQL:

npm install pg pg-query-stream # pg-query-stream is optional, used in .stream() method

MySQL:

npm install mysql2 # or mysql

MS SQL Server (MSSQL):

npm install tedious

SQLite:

npm install better-sqlite3 # or sqlite3

If you have already defined your Knex Tables interface, you can convert it using the KyselifyTables type:

src/types/database.ts:

import type {Tables} from 'knex/types/tables'
import type {KyselifyTables} from 'kysely-knex'

export type Database = KyselifyTables<Tables>

Otherwise, refer to the Kysely documentation for more information.

Create a Kysely instance. Pass it your existing Knex instance:

src/kysely.ts:

import {Kysely} from 'kysely'
import {KyselyKnexDialect, PGColdDialect} from 'kysely-knex'
import {knex} from './knex'
import type {Database} from './types/database'

export const kysely = new Kysely<Database>({
  dialect: new KyselyKnexDialect({
    knex,
    kyselySubDialect: new PGColdDialect(),
  }),
})

For other dialects, simply swap PGColdDialect with MySQLColdDialect, MySQL2ColdDialect, MSSQLColdDialect, SQLite3ColdDialect or BetterSQLite3ColdDialect.

There are a few ways to tackle migrations given you have an existing Knex migration setup:

1. Delete all existing migrations and start fresh with Kysely migrations.
2. Use our custom migration source KyselyFsMigrationSource to provide a Kysely instance to your Knex-managed migrations:

migrations/20240101000000_add_email_column.ts:

import type {Knex} from 'knex'
import type {Kysely} from 'kysely'

export async function up(_: Knex, kysely: Kysely<any>): Promise<void> {
  await kysely.schema
    .alterTable('dog_walker')
    .addColumn('email', 'varchar', (cb) => cb.unique())
    .execute()
}

export async function down(_: Knex, kysely: Kysely<any>): Promise<void> {
  await kysely.schema.alterTable('dog_walker').dropColumn('email').execute()
}

Pass the migration source to all migrate commands as follows:

scripts/migrate-to-latest.ts:

import {join} from 'node:path'
import {KyselyFsMigrationSource} from 'kysely-knex'
import {knex} from '../src/knex'
import {kysely} from '../src/kysely'

export const migrationSource = new KyselyFsMigrationSource({
  migrationDirectories: join(__dirname, '../migrations'),
})

await knex.migrate.latest({migrationSource})

or pass it to Knex CLI globally:

knexfile.ts:

const {KyselyFsMigrationSource, PGColdDialect} = require('kysely-knex')

module.exports = {
  // ...
  migrations: {
    // ...
    migrationSource: new KyselyFsMigrationSource({
      kyselySubDialect: new PGColdDialect(),
      migrationDirectories: 'migrations',
    }),
    // ...
  },
  // ...
}

This'll allow you to seamlessly transition to only use Kysely from a certain point in time. Then, you could gradually convert existing Knex migration files to use Kysely instead of Knex, as all migrations now receive a Kysely instance.

More ways to tackle this topic might be provided in the future. Stay tuned!