Schema migration with Neon Postgres and Drizzle ORM

Drizzle is a TypeScript-first ORM that connects to all major databases and works across most Javascript runtimes. It provides a simple way to define database schemas and queries in an SQL-like dialect and tools to generate and run migrations.

This guide shows how to use Drizzle with the Neon Postgres database in a Typescript project. We'll create a simple Node.js application with Hono.js and demonstrate the full workflow of setting up and working with your database using Drizzle.

Prerequisites

To follow along with this guide, you will need:

• A Neon account. If you do not have one, sign up at Neon. Your Neon project comes with a ready-to-use Postgres database named neondb. We'll use this database in the following examples.
• Node.js and npm installed on your local machine. We'll use Node.js to build and test the application locally.

Setting up your Neon database

Initialize a new project

1. Log in to the Neon Console and navigate to the Projects section.
2. Select a project or click the New Project button to create a new one.

Retrieve your Neon database connection string

Navigate to the Connection Details section to find your database connection string. It should look similar to this:

postgres://alex:AbC123dEf@ep-cool-darkness-123456.us-east-2.aws.neon.tech/dbname?sslmode=require

Keep your connection string handy for later use.

Setting up the TypeScript application

Create a new Hono.js project

We'll create a simple catalog, with API endpoints that query the database for authors and a list of their books. Run the following command in your terminal to set up a new project using Hono.js:

npm create hono@latest neon-drizzle-guide

This initiates an interactive CLI prompt to set up a new project. To follow along with this guide, you can use the following settings:

Need to install the following packages:
create-hono@0.9.0
Ok to proceed? (y) y

create-hono version 0.9.0
✔ Using target directory … neon-drizzle-guide
✔ Which template do you want to use? › nodejs
cloned honojs/starter#main to ./repos/javascript/neon-drizzle-guide
✔ Do you want to install project dependencies? … yes
✔ Which package manager do you want to use? › npm

To use Drizzle and connect to the Neon database, we also add the drizzle-orm and drizzle-kit packages to our project, along with the Neon serverless driver library.

cd neon-drizzle-guide && touch .env
npm install drizzle-orm @neondatabase/serverless
npm install -D drizzle-kit dotenv

Add the DATABASE_URL environment variable to your .env file, which you'll use to connect to our Neon database. Use the connection string that you obtained from the Neon Console earlier:

# .env
DATABASE_URL=NEON_DATABASE_CONNECTION_STRING

Test that the starter Hono.js application works by running npm run dev in the terminal. You should see the Hello, Hono! message when you navigate to http://localhost:3000 in your browser.

Set up the database schema

Now, we will define the schema for the application using the Drizzle ORM. Create a new schema.ts file in your src directory and add the following code:

// src/schema.ts

import { pgTable, integer, serial, text, timestamp } from 'drizzle-orm/pg-core';

export const authors = pgTable('authors', {
  id: serial('id').primaryKey(),
  name: text('name').notNull(),
  bio: text('bio'),
  createdAt: timestamp('created_at').notNull().defaultNow(),
});

export const books = pgTable('books', {
  id: serial('id').primaryKey(),
  title: text('title').notNull(),
  authorId: integer('author_id').references(() => authors.id),
  createdAt: timestamp('created_at').notNull().defaultNow(),
});

The code defines two tables: authors, which will contain the list of all the authors, and books, which will contain the list of books written by the authors. Each book is associated with an author using the authorId field.

To generate a migration to create these tables in the database, we'll use the drizzle-kit command. Add the following script to the package.json file at the root of your project:

{
  "scripts": {
    "db:generate": "drizzle-kit generate --dialect=postgresql --schema=src/schema.ts --out=./drizzle"
  }
}

Then, run the following command in your terminal to generate the migration files:

npm run db:generate

This command generates a new folder named drizzle containing the migration files for the authors and books tables.

Run the migration

The generated migration file is written in SQL and contains the necessary commands to create the tables in the database. To apply these migrations, we'll use the Neon serverless driver and helper functions provided by the drizzle-orm library.

Create a new migrate.ts in your src directory and add the following code:

// src/migrate.ts

import { drizzle } from 'drizzle-orm/neon-http';
import { neon } from '@neondatabase/serverless';
import { migrate } from 'drizzle-orm/neon-http/migrator';
import { config } from 'dotenv';

config({ path: '.env' });

const sql = neon(process.env.DATABASE_URL!);
const db = drizzle(sql);

const main = async () => {
  try {
    await migrate(db, { migrationsFolder: 'drizzle' });
    console.log('Migration completed');
  } catch (error) {
    console.error('Error during migration:', error);
    process.exit(1);
  }
};

main();

The drizzle-orm package comes with an integration for Neon, which allows us to run the migrations using the migrate function. Add a new script to the package.json file that executes the migration.

{
  "scripts": {
    "db:migrate": "tsx ./src/migrate.ts"
  }
}

You can now run the migration script using the following command:

npm run db:migrate

You should see the Migration completed message in the terminal, indicating that the migration was successful.

Seed the database

To test the application works, we need to add some example data to our tables. Create a new file at src/seed.ts and add the following code to it:

// src/seed.ts

import { drizzle } from 'drizzle-orm/neon-http';
import { neon } from '@neondatabase/serverless';
import { authors, books } from './schema';
import { config } from 'dotenv';

config({ path: '.env' });

const sql = neon(process.env.DATABASE_URL!);
const db = drizzle(sql);

async function seed() {
  await db.insert(authors).values([
    {
      name: 'J.R.R. Tolkien',
      bio: 'The creator of Middle-earth and author of The Lord of the Rings.',
    },
    {
      name: 'George R.R. Martin',
      bio: 'The author of the epic fantasy series A Song of Ice and Fire.',
    },
    {
      name: 'J.K. Rowling',
      bio: 'The creator of the Harry Potter series.',
    },
  ]);

  const authorRows = await db.select().from(authors);
  const authorIds = authorRows.map((row) => row.id);

  await db.insert(books).values([
    {
      title: 'The Fellowship of the Ring',
      authorId: authorIds[0],
    },
    {
      title: 'The Two Towers',
      authorId: authorIds[0],
    },
    {
      title: 'The Return of the King',
      authorId: authorIds[0],
    },
    {
      title: 'A Game of Thrones',
      authorId: authorIds[1],
    },
    {
      title: 'A Clash of Kings',
      authorId: authorIds[1],
    },
    {
      title: "Harry Potter and the Philosopher's Stone",
      authorId: authorIds[2],
    },
    {
      title: 'Harry Potter and the Chamber of Secrets',
      authorId: authorIds[2],
    },
  ]);
}

async function main() {
  try {
    await seed();
    console.log('Seeding completed');
  } catch (error) {
    console.error('Error during seeding:', error);
    process.exit(1);
  }
}

main();

This script inserts some seed data into the authors and books tables. Add a new script to the package.json file that runs the seeding program.

{
  "scripts": {
    "db:seed": "tsx ./src/seed.ts"
  }
}

Run the seed script using the following command:

npm run db:seed

You should see the Seeding completed message in the terminal, indicating that the seed data was inserted into the database.

Implement the API endpoints

Now that the database is set up and populated with data, we can implement the API to query the authors and their books. Replace the existing src/index.ts file with the following code:

// src/index.ts

import { serve } from '@hono/node-server';
import { Hono } from 'hono';
import { env } from 'hono/adapter';
import { config } from 'dotenv';

import { eq } from 'drizzle-orm';
import { drizzle } from 'drizzle-orm/neon-http';
import { neon } from '@neondatabase/serverless';
import { authors, books } from './schema';

config({ path: '.env' });
const app = new Hono();

app.get('/', (c) => {
  return c.text('Hello, this is a catalog of books!');
});

app.get('/authors', async (c) => {
  const { DATABASE_URL } = env<{ DATABASE_URL: string }>(c);
  const sql = neon(DATABASE_URL);
  const db = drizzle(sql);

  const output = await db.select().from(authors);
  return c.json(output);
});

app.get('/books/:authorId', async (c) => {
  const { DATABASE_URL } = env<{ DATABASE_URL: string }>(c);
  const sql = neon(DATABASE_URL);
  const db = drizzle(sql);

  const authorId = c.req.param('authorId');
  const output = await db
    .select()
    .from(books)
    .where(eq(books.authorId, Number(authorId)));
  return c.json(output);
});

const port = 3000;
console.log(`Server is running on port ${port}`);

serve({
  fetch: app.fetch,
  port,
});

This code sets up a simple API with two endpoints: /authors and /books/:authorId. The /authors endpoint returns a list of all the authors, and the /books/:authorId endpoint returns a list of books written by the specific author with the given authorId.

Run the application using the following command:

npm run dev

This will start a Hono.js server at http://localhost:3000. Navigate to http://localhost:3000/authors and http://localhost:3000/books/1 in your browser to check that the API works as expected.

Migration after a schema change

To demonstrate how to execute a schema change, we'll add a new column to the authors table, listing the country of origin for each author.

Generate the new migration

Modify the code in the src/schema.ts file to add the new column to the authors table:

// src/schema.ts

import { pgTable, integer, serial, text, timestamp } from 'drizzle-orm/pg-core';

export const authors = pgTable('authors', {
  id: serial('id').primaryKey(),
  name: text('name').notNull(),
  bio: text('bio'),
  country: text('country'),
  createdAt: timestamp('created_at').notNull().defaultNow(),
});

export const books = pgTable('books', {
  id: serial('id').primaryKey(),
  title: text('title').notNull(),
  authorId: integer('author_id').references(() => authors.id),
  createdAt: timestamp('created_at').notNull().defaultNow(),
});

Now, we can run the following command to generate a new migration file:

npm run db:generate

This command generates a new migration file in the drizzle folder, with the SQL command to add the new column to the authors table.

Run the migration

Run the migration script using the following command:

npm run db:migrate

You should see the Migration completed message in the terminal, indicating it was successful.

Verify the schema change

To verify that the schema change was successful, run the application using the following command:

npm run dev

You can navigate to http://localhost:3000/authors in your browser to check that each author entry has a country field, currently set to null.

Conclusion

In this guide, we set up a new TypeScript project using Hono.js and Drizzle ORM and connected it to a Neon Postgres database. We created a schema for the database, generated and ran migrations, and implemented API endpoints to query the database.

Source code

You can find the source code for the application described in this guide on GitHub.

• Migrations with Neon and Drizzle

  Run Neon database migrations using Drizzle

Resources

For more information on the tools used in this guide, refer to the following resources:

• Drizzle ORM
• Hono.js