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Getting started

Installation​

Kysely can be installed using any of the following package managers:

npm is the default package manager for Node.js, and to where Kysely is published.
Your project is using npm if it has a package-lock.json file in its root folder.

Run the following command in your terminal:

terminal
npm install kysely

Types​

For Kysely's type-safety and autocompletion to work, it needs to know your database structure. This requires a TypeScript Database interface, that contains table names as keys and table schema interfaces as values.

Let's define our first database interface:

src/types.ts
import {
  ColumnType,
  Generated,
  Insertable,
  JSONColumnType,
  Selectable,
  Updateable
} from 'kysely'

export interface Database {
  person: PersonTable
  pet: PetTable
}

// This interface describes the `person` table to Kysely. Table
// interfaces should only be used in the `Database` type above
// and never as a result type of a query!. See the `Person`,
// `NewPerson` and `PersonUpdate` types below.
export interface PersonTable {
  // Columns that are generated by the database should be marked
  // using the `Generated` type. This way they are automatically
  // made optional in inserts and updates.
  id: Generated<number>

  first_name: string
  gender: 'man' | 'woman' | 'other'

  // If the column is nullable in the database, make its type nullable.
  // Don't use optional properties. Optionality is always determined
  // automatically by Kysely.
  last_name: string | null

  // You can specify a different type for each operation (select, insert and
  // update) using the `ColumnType<SelectType, InsertType, UpdateType>`
  // wrapper. Here we define a column `created_at` that is selected as
  // a `Date`, can optionally be provided as a `string` in inserts and
  // can never be updated:
  created_at: ColumnType<Date, string | undefined, never>

  // You can specify JSON columns using the `JSONColumnType` wrapper.
  // It is a shorthand for `ColumnType<T, string, string>`, where T
  // is the type of the JSON object/array retrieved from the database,
  // and the insert and update types are always `string` since you're
  // always stringifying insert/update values.
  metadata: JSONColumnType<{
    login_at: string;
    ip: string | null;
    agent: string | null;
    plan: 'free' | 'premium';
  }>
}

// You should not use the table schema interfaces directly. Instead, you should
// use the `Selectable`, `Insertable` and `Updateable` wrappers. These wrappers
// make sure that the correct types are used in each operation.
//
// Most of the time you should trust the type inference and not use explicit
// types at all. These types can be useful when typing function arguments.
export type Person = Selectable<PersonTable>
export type NewPerson = Insertable<PersonTable>
export type PersonUpdate = Updateable<PersonTable>

export interface PetTable {
  id: Generated<number>
  name: string
  owner_id: number
  species: 'dog' | 'cat'
}

export type Pet = Selectable<PetTable>
export type NewPet = Insertable<PetTable>
export type PetUpdate = Updateable<PetTable>
Codegen

For production apps, it is recommended to automatically generate your Database interface by introspecting your production database or Prisma schemas. Generated types might differ in naming convention, internal order, etc. Find out more at "Generating types".

Runtime types

Kysely only deals with types in the typescript level. The runtime javascript types are decided by the underlying 3rd party driver such as pg or mysql2 and it's up to you to select the correct typescript types in the database interface. Kysely never touches the runtime output types in any way. Find out more at "Data types".

Dialects​

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Instantiation​

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Querying​

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Summary​

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