Kysely - Prisma — ContextQMD

Kysely is a type-safe TypeScript SQL query builder that provides TypeScript support and a fluent API for building SQL queries. In this guide, you'll learn how to connect Kysely to Prisma Postgres and start querying your database with full type safety.

Prerequisites

Node.js version 14 or higher
TypeScript version 4.6 or higher (5.4+ recommended for improved type inference, 5.9+ for better compilation performance)
Strict mode enabled in your tsconfig.json for Kysely's type safety

1. Create a new project

Create a new directory for your project and initialize it with npm:

npm

mkdir kysely-quickstart
cd kysely-quickstart
npm init -y

Install TypeScript and initialize it:

npm

npm install --save-dev typescript

npm

npx tsc --init

2. Configure TypeScript

Kysely requires TypeScript's strict mode for proper type safety. Update your tsconfig.json file:

json

{
  // ...
  "compilerOptions": {
    // ...
    "strict": true, // [!code ++]
    "allowImportingTsExtensions": true, // [!code ++]
    "noEmit": true // [!code ++]
    // ...
  }
  // ...
}

:::note

The strict: true setting is required for Kysely's type safety to work correctly.

:::

In your package.json, set the type to module:

json

{
  // ...
  "type": "module" // [!code ++]
  // ...
}

3. Create a Prisma Postgres database

You can create a Prisma Postgres database using the create-db CLI tool. Follow these steps to create your Prisma Postgres database:

npm

npx create-db

Then the CLI tool should output:

bash

┌  🚀 Creating a Prisma Postgres database
│
│  Provisioning a temporary database in us-east-1...
│
│  It will be automatically deleted in 24 hours, but you can claim it.
│
◇  Database created successfully!
│
│
●  Database Connection
│
│
│    Connection String:
│
│    postgresql://hostname:[email protected]:5432/postgres?sslmode=require
│
│
◆  Claim Your Database
│
│    Keep your database for free:
│
│    https://create-db.prisma.io/claim?CLAIM_CODE
│
│    Database will be deleted on 11/18/2025, 1:55:39 AM if not claimed.
│
└

Create a .env file and add the connection string from the output:

text

DATABASE_URL="postgresql://hostname:[email protected]:5432/postgres?sslmode=require"

:::warning

Never commit .env files to version control. Add .env to your .gitignore file to keep credentials secure.

:::

The database created is temporary and will be deleted in 24 hours unless claimed. Claiming moves the database into your Prisma Data Platform account. Visit the claim URL from the output to keep your database.

:::note

To learn more about the create-db CLI tool, see the create-db documentation.

:::

4. Install dependencies

Install Kysely and the PostgreSQL driver:

npm

npm install kysely pg dotenv

npm

npm install --save-dev @types/pg tsx

Package breakdown:

kysely: The type-safe SQL query builder
pg: PostgreSQL driver for Node.js (required by Kysely's PostgresDialect)
dotenv: Loads environment variables from .env file
@types/pg: TypeScript type definitions for the pg driver
tsx: TypeScript execution engine for running .ts files directly

5. Define database types

Create a src/types.ts file to define your database schema types:

typescript

import type { Generated } from "kysely";

export interface Database {
  users: UsersTable;
}

export interface UsersTable {
  id: Generated<number>;
  email: string;
  name: string | null;
}

6. Configure database connection

Create a src/database.ts file to instantiate Kysely with your Prisma Postgres connection:

typescript

import "dotenv/config";
import type { Database } from "./types.ts";
import { Pool } from "pg";
import { Kysely, PostgresDialect } from "kysely";

// Parse DATABASE_URL into connection parameters
function parseConnectionString(url: string) {
  const parsed = new URL(url);
  return {
    host: parsed.hostname,
    port: parseInt(parsed.port),
    user: parsed.username,
    password: parsed.password,
    database: parsed.pathname.slice(1), // Remove leading '/'
  };
}

const connectionParams = parseConnectionString(process.env.DATABASE_URL!);

const dialect = new PostgresDialect({
  pool: new Pool({
    ...connectionParams,
    ssl: true,
    max: 10,
  }),
});

// Database interface is passed to Kysely's constructor, and from now on, Kysely
// knows your database structure.
// Dialect is passed to Kysely's constructor, and from now on, Kysely knows how
// to communicate with your database.
export const db = new Kysely<Database>({
  dialect,
});

7. Run queries

Create a src/script.ts file:

typescript

import { db } from "./database.ts";

async function main() {
  // Create the users table
  await db.schema
    .createTable("users")
    .ifNotExists()
    .addColumn("id", "serial", (col) => col.primaryKey())
    .addColumn("email", "varchar(255)", (col) => col.notNull().unique())
    .addColumn("name", "varchar(255)")
    .execute();

  // Insert a user
  const user = await db
    .insertInto("users")
    .values({
      email: "[email protected]",
      name: "Alice",
    })
    .returningAll()
    .executeTakeFirstOrThrow();

  console.log("Created user:", user);

  // Query all users
  const users = await db.selectFrom("users").selectAll().execute();

  console.log("All users:", users);
}

main()
  .then(async () => {
    await db.destroy();
  })
  .catch(async (error) => {
    console.error("Error:", error);
    await db.destroy();
    process.exit(1);
  });

Run the script:

npm

npx tsx src/script.ts

You should receive the following output:

bash

Created user: { id: 1, email: '[email protected]', name: 'Alice' }
All users: [ { id: 1, email: '[email protected]', name: 'Alice' } ]

Next steps

You've successfully connected Kysely to Prisma Postgres! For more advanced features like schemas, migrations, and complex queries, see the Kysely documentation.