kysely-sequelize

Sequelize is a modern TypeScript and Node.js ORM for Oracle, Postgres, MySQL, MariaDB, SQLite and SQL Server, and more. Featuring solid transaction support, relations, eager and lazy loading, read replication and more.

As of Mar 16, 2024, Sequelize is gearing up for v7 (currently in alpha) and has 2,107,202 weekly downloads on npm (most popular ORM). It is a very popular ORM for Node.js and TypeScript (thanks to sequelize-typescript).

Just like most ORMs for Node.js, Sequelize has poor TypeScript support when it comes to writing queries outside of the ORM's CRUD methods - something that happens more often than you might imagine - usually due to performance optimizations OR as a general escape hatch. This is where Kysely comes in.

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.

A match made in heaven, on paper. Let’s see how it works in practice, with kysely-sequelize - a toolkit (dialect, type translators, etc.) that allows using your existing Sequelize instance with Kysely.

Installation

Main dependencies:

npm i kysely kysely-sequelize sequelize sequelize-typescript

PostgreSQL:

npm i pg

MySQL:

npm i mysql2

MS SQL Server (MSSQL):

npm i tedious

SQLite:

ATTTENTION: While Kysely supports better-sqlite3 with its core SQLite dialect, Sequelize uses sqlite3 under the hood. This library doesn't use Kysely's own drivers.

npm i sqlite3

Usage

Models & Types

As of today, there are two ways to define Sequelize models in TypeScript. This library supports both.

Sequelize >= v6.14.0

Define your model with InferAttributes, InferCreationAttributes, CreationOptional, NonAttribute, ForeignKey, etc.

src/models/person.model.ts:

import type {GeneratedAlways} from 'kysely-sequelize'
import type {CreationOptional, InferAttributes, InferCreationAttributes, NonAttribute} from 'sequelize'
import {Column, DataType, HasMany, Model, Table} from 'sequelize-typescript'
import {PetModel} from './pet.model'

@Table({modelName: 'Person', tableName: 'person', timestamps: false, underscored: true})
export class PersonModel extends Model<InferAttributes<PersonModel>, InferCreationAttributes<PersonModel>> {
  declare id: GeneratedAlways<CreationOptional<number>>

  @Column(DataType.STRING(255))
  firstName: string | null

  @Column(DataType.STRING(255))
  middleName: string | null

  @Column(DataType.STRING(255))
  lastName: string | null

  @Column({allowNull: false, type: DataType.STRING(50)})
  gender: 'male' | 'female' | 'other'

  @Column(DataType.STRING(50))
  maritalStatus: 'single' | 'married' | 'divorced' | 'widowed' | null

  @HasMany(() => PetModel)
  pets: NonAttribute<PetModel[]>
}

src/models/pet.model.ts:

import type {CreationOptional, ForeignKey, InferAttributes, InferCreationAttributes, NonAttribute} from 'sequelize'
import {BelongsTo, Column, DataType, HasMany, Model, Table} from 'sequelize-typescript'
import {PersonModel} from './person.model.js'
import {ToyModel} from './toy.model.js'

@Table({
  modelName: 'Pet',
  indexes: [{fields: ['owner_id'], name: 'pet_owner_id_index'}],
  tableName: 'pet',
  timestamps: false,
  underscored: true,
})
export class PetModel extends Model<InferAttributes<PetModel>, InferCreationAttributes<PetModel>> {
  declare id: GeneratedAlways<CreationOptional<number>>

  @Column({allowNull: false, type: DataType.STRING(255)})
  name: string

  declare ownerId: ForeignKey<number>

  @Column({allowNull: false, type: DataType.STRING(50)})
  species: 'dog' | 'cat' | 'hamster'

  @BelongsTo(() => PersonModel, 'ownerId')
  owner: NonAttribute<PersonModel>

  @HasMany(() => ToyModel)
  toys: NonAttribute<ToyModel[]>
}

src/models/toy.model.ts:

import type {CreationOptional, ForeignKey, InferAttributes, InferCreationAttributes, NonAttribute} from 'sequelize'
import {BelongsTo, Column, DataType, Model, Table} from 'sequelize-typescript'
import {PetModel} from './pet.model'

export interface ToyAttributes {
  id: number
  name: string
  price: number
  petId: number
}

export type ToyCreationAttributes = Optional<ToyAttributes, 'id'>

@Table({modelName: 'Toy', tableName: 'toy', timestamps: false, underscored: true})
export class ToyModel extends Model<InferAttributes<ToyModel>, InferCreationAttributes<ToyModel>> {
  declare id: GeneratedAlways<CreationOptional<number>>

  @Column({allowNull: false, type: DataType.STRING(255)})
  name: string

  declare petId: ForeignKey<number>

  @Column({allowNull: false, type: DataType.DOUBLE})
  price: number

  @BelongsTo(() => PetModel, 'petId')
  pet: NonAttribute<PetModel>
}

Use KyselifyModel to transform your Sequelize models into Kysely-compatible table schema.

src/types/database.ts:

import type {KyselifyModel} from 'kysely-sequelize'
import type {PersonModel, PetModel, ToyModel} from '../models'

export type PersonTable = KyselifyModel<PersonModel>
//              ^? { id: GeneratedAlways<number>, firstName: string | null, ... }
export type PetTable = KyselifyModel<PetCreationAttributes>
export type ToyTable = KyselifyModel<ToyCreationAttributes>

export interface Database {
  person: PersonTable
  pet: PetTable
  toy: ToyTable
}

Sequelize < v6.14.0 (the old verbose way)

Define your models using sequelize-typescript and manual attribute typing.

src/models/person.model.ts:

import type {Optional} from 'sequelize'
import {Column, DataType, HasMany, Model, Table} from 'sequelize-typescript'
import {PetModel} from './pet.model'

export interface PersonAttributes {
  id: number
  firstName: string | null
  middleName: string | null
  lastName: string | null
  gender: 'male' | 'female' | 'other'
  maritalStatus: 'single' | 'married' | 'divorced' | 'widowed' | null
}

export type PersonCreationAttributes = Optional<PersonAttributes, 'id'>

@Table({modelName: 'Person', tableName: 'person', timestamps: false, underscored: true})
export class PersonModel extends Model<PersonAttributes, PersonCreationAttributes> {
  declare id: PersonAttributes['id']

  @Column(DataType.STRING(255))
  firstName: PersonAttributes['firstName']

  @Column(DataType.STRING(255))
  middleName: PersonAttributes['middleName']

  @Column(DataType.STRING(255))
  lastName: PersonAttributes['lastName']

  @Column({allowNull: false, type: DataType.STRING(50)})
  gender: PersonAttributes['gender']

  @Column(DataType.STRING(50))
  maritalStatus: PersonAttributes['maritalStatus']

  @HasMany(() => PetModel)
  pets: PetModel[]
}

src/models/pet.model.ts:

import type {Optional} from 'sequelize'
import {BelongsTo, Column, DataType, ForeignKey, HasMany, Model, Table} from 'sequelize-typescript'
import {PersonModel} from './person.model.js'
import {ToyModel} from './toy.model.js'

export interface PetAttributes {
  id: number
  name: string
  ownerId: number
  species: 'dog' | 'cat' | 'hamster'
}

export type PetCreationAttributes = Optional<PetAttributes, 'id'>

@Table({
  modelName: 'Pet',
  indexes: [{fields: ['owner_id'], name: 'pet_owner_id_index'}],
  tableName: 'pet',
  timestamps: false,
  underscored: true,
})
export class PetModel extends Model<PetAttributes, PetCreationAttributes> {
  declare id: PetAttributes['id']

  @Column({allowNull: false, type: DataType.STRING(255)})
  name: PetAttributes['name']

  @Column({allowNull: false, onDelete: 'CASCADE', type: DataType.INTEGER})
  @ForeignKey(() => PersonModel)
  ownerId: PetAttributes['ownerId']

  @Column({allowNull: false, type: DataType.STRING(50)})
  species: PetAttributes['species']

  @BelongsTo(() => PersonModel)
  owner: PersonModel

  @HasMany(() => ToyModel)
  toys: ToyModel[]
}

src/models/toy.model.ts:

import type {Optional} from 'sequelize'
import {BelongsTo, Column, DataType, ForeignKey, Model, Table} from 'sequelize-typescript'
import {PetModel} from './pet.model'

export interface ToyAttributes {
  id: number
  name: string
  price: number
  petId: number
}

export type ToyCreationAttributes = Optional<ToyAttributes, 'id'>

@Table({modelName: 'Toy', tableName: 'toy', timestamps: false, underscored: true})
export class ToyModel extends Model<ToyAttributes, ToyCreationAttributes> {
  declare id: ToyAttributes['id']

  @Column({allowNull: false, type: DataType.STRING(255)})
  name: ToyAttributes['name']

  @Column({allowNull: false, type: DataType.INTEGER})
  @ForeignKey(() => PetModel)
  petId: ToyAttributes['petId']

  @Column({allowNull: false, type: DataType.DOUBLE})
  price: ToyAttributes['price']

  @BelongsTo(() => PetModel)
  pet: PetModel
}

Use KyselifyCreationAttributes to transform your Sequelize models' attributes into Kysely-compatible types.

src/types/database.ts:

import type {KyselifyCreationAttributes} from 'kysely-sequelize'
import type {PersonCreationAttributes, PetCreationAttributes, ToyCreationAttributes} from '../models'

export type PersonTable = KyselifyCreationAttributes<PersonCreationAttributes>
//              ^? { id: GeneratedAlways<number>, firstName: string | null, ... }
export type PetTable = KyselifyCreationAttributes<PetCreationAttributes>
export type ToyTable = KyselifyCreationAttributes<ToyCreationAttributes>

export interface Database {
  person: PersonTable
  pet: PetTable
  toy: ToyTable
}

Sequelize Instance

Create a Sequelize instance.

src/sequelize.ts:

import {Sequelize} from 'sequelize-typescript'
import {PersonModel, PetModel, ToyModel} from './models'

let sequelize: Sequelize

async function getSequelize(): Promise<Sequelize> {
  if (sequelize) {
    return sequelize
  }

  // this create a new Sequelize instance for Postgres
  // kysely-sequelize also supports MySQL, SQLite, and MS SQL Server.
  const sqlz = new Sequelize({
    database: '{{database}}',
    dialect: 'postgres',
    host: '{{host}}',
    models: [PersonModel, PetModel, ToyModel],
    pool: {max: 20, min: 0},
    port: 5434,
    username: '{{username}}',
  })

  await sqlz.authenticate({
    retry: {
      backoffBase: 1_000,
      backoffExponent: 1,
      max: (5 * 60 * 1_000) / 5,
      timeout: 5 * 60 * 1_000,
    },
  })

  await sequelize.sync()

  sequelize = sqlz
}

Kysely Instance

Create a Kysely instance.

src/kysely.ts:

import {CamelCasePlugin, Kysely, PostgresAdapter, PostgresIntrospector, PostgresQueryCompiler} from 'kysely'
import {KyselySequelizeDialect} from 'kysely-sequelize'
import type {Database} from './types/database'

let kysely: Kysely<Database>

async function getKysely(): Promise<Kysely<Database>> {
  if (kysely) {
    return kysely
  }

  const sequelize = await getSequelize()

  kysely = new Kysely<Database>({
    dialect: new KyselySequelizeDialect({
      // kysely-sequelize also supports MySQL, SQLite, and MS SQL Server.
      // Since Kysely's MS SQL Server dialect is unreleased, you'll have to install Kysely directly from Github for now.
      kyselyDialect: {
        createAdapter: () => PostgresAdapter(),
        createIntrospector: (db) => new PostgresIntrospector(db),
        createQueryCompiler: () => new PostgresQueryCompiler(),
      },
      sequelize,
    }),
    // `CamelCasePlugin` is used to align with Sequelize's `underscored` option.
    plugins: [new CamelCasePlugin()],
  })

  return kysely
}