[BUG] Prisma throws `Error: [unenv] fs.readdir is not implemented yet!` when querying

[schweetheart]

Describe the bug

After following the Cloudflare workers with PostgreSQL tutorial.

When making a query via prisma client Error: [unenv] fs.readdir is not implemented yet! is thrown when running via the workers runtime pnpm preview.

When using a worker directly, Prisma works correctly.

// schema.prisma
generator client {
  provider        = "prisma-client-js"
  previewFeatures = ["driverAdapters"]
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

model Post {
  id        Int      @id @default(autoincrement())
  title     String
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt
}

// page.tsx
export default async function Home() {
  
// Force SSR
  connection();

  const connectionString = "example"

  const adapter = new PrismaPg({ connectionString });
  const prisma = new PrismaClient({ adapter });

  const posts = await prisma.post.findMany();
  return (
    <div>
      <div>{Date()}</div>
      <div>{JSON.stringify(posts)}</div>
    </div>
  );
} 

Steps to reproduce

1. Clone the minimal reproduction
2. Set DATABASE_URL in .env and .dev.vars with a postgres compatible database. (I used Neon)
3. Preview the app locally via pnpm preview
4. Visit http://localhost:3000/
5. You should see the error in the dialog.

Expected behavior

When running prisma directly in a worker without OpenNext, with the same code the result is working. When running the same code with OpenNext, the error is thrown.
Am I missing some configuration, or is there some unexpected behavior when the OpenNext build process interacts with Prisma.

@opennextjs/cloudflare version

1.0.0-beta.4

Wrangler version

4.14.0

next info output

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.4.0: Fri Apr 11 18:33:47 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T6000
  Available memory (MB): 16384
  Available CPU cores: 8
Binaries:
  Node: 20.11.1
  npm: 10.8.1
  Yarn: 1.22.19
  pnpm: 9.15.0
Relevant Packages:
  next: 15.3.1 // Latest available version is detected (15.3.1).
  eslint-config-next: 15.3.1
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A

Additional context

Setting PRISMA_CLIENT_FORCE_WASM=1 has had no effect. I also tested via the @prisma/adapter-neon adapter with the same error.

It looks like others have encountered the same error recently with different adapters.

[vicb]

At least @prisma/client uses the workerd build condition.

Hopefully #593 should help with that - it has not been released yet but you can try the OpenNext binary from the PR.

You have to add the workerd specific packages to serverExternalPackages . See #548 for some info. We will document that over the next few days.

Hope this helps

[schweetheart]

Appreciate the quick response!

I've followed your suggestion and given the #593 binary a try and updated serverExternalPackages with the related packages, however am still getting the same error message. Have I missed some config somewhere?

// `@prisma/client` and `pg` are included in the Next.js serverExternalPackages list and should
//  automatically be opt-ed out
// https://github.com/vercel/next.js/blob/canary/packages/next/src/lib/server-external-packages.json
const nextConfig: NextConfig = {
  serverExternalPackages: ["@prisma/adapter-pg", "pg", "@prisma/client"],
};

Repro

[conico974]

No there is some other issue specific to prisma. Will have a PR for it tomorrow

[schweetheart]

All working correctly for me after #628!

[vicb]

@schweetheart thanks for reporting and of course thanks to @conico974 for fixing that!

[Noitidart]

Even with #628 it's not working for me. I even tried upgrading to latest "@opennextjs/cloudflare": "^1.3.0", I get the same readdir issue.

[Noitidart]

I have created a minimum reproducible - https://github.com/Noitidart/prisma-fail-cf-workers-nextjs

Can try running npm run preview and then hitting http://localhost:8787/api/hello and you will see:

{
  "name": "Error",
  "error": "[unenv] fs.readdir is not implemented yet!"
}

I attached a .env.sample but can change that to any connection url.

[BearTyree]

I am having this same issue when attempting to use Prisma with cf workers and NextJs. Any updates? My repository is here: https://github.com/BearTyree/Flash-Royale I have the driver adapters enabled in my prisma schema, why is prisma trying to access the fs on the edge?

[sommeeeer]

@BearTyree @Noitidart

Remember to add this to your next config:

const nextConfig: NextConfig = {
  // note both the `@prisma/client` and `.prisma/client`
  // you also want the adapters here
  serverExternalPackages: ["@prisma/adapter-neon", "@neondatabase/serverless", "@prisma/client", ".prisma/client"],
};

[Noitidart]

Thanks @sommeeeer I did that here https://github.com/Noitidart/prisma-fail-cf-workers-nextjs/blob/master/next.config.ts

But still same