Mocking Your Postgres DB Doesn't Have to Suck

#prisma #webdev #fakerjs #postgres

We’ve all been there: you’re building a beautiful Express API, but your frontend looks like a ghost town because your database is empty. You spend 20 minutes manually typing test@test.com into TablePlus just to see if your CSS breaks.

Stop doing that.

By combining Faker.js with Prisma, we can create a "Reset Button" for our local environment that wipes the junk and seeds 100+ realistic records in seconds.

The Stack

Database: PostgreSQL
ORM: Prisma
Mocking: @faker-js/faker
Server: Express + TypeScript

1. Install the Secret Sauce

You don’t want Faker in your production bundle. Keep it in devDependencies.

npm install @faker-js/faker --save-dev

2. The "Nuke & Pave" Script

Create a file at prisma/seed.ts. This script does two things: it cleans the database (to prevent unique constraint errors) and populates it.

import { PrismaClient } from '@prisma/client';
import { faker } from '@faker-js/faker';

const prisma = new PrismaClient();

async function main() {
  console.log("⚡ Starting database refresh...");

  // --- THE REMOVER ---
  // Note: Delete 'many' in order of dependency (Posts first, then Users)
  await prisma.post.deleteMany();
  await prisma.user.deleteMany();
  console.log("🧹 Database wiped.");

  // --- THE SEEDER ---
  const userCount = 10;

  for (let i = 0; i < userCount; i++) {
    await prisma.user.create({
      data: {
        email: faker.internet.email(),
        name: faker.person.fullName(),
        avatar: faker.image.avatar(),
        posts: {
          create: [
            { title: faker.lorem.sentence(), content: faker.lorem.paragraphs(2) },
            { title: faker.lorem.sentence(), content: faker.lorem.paragraphs(2) },
          ],
        },
      },
    });
  }

  console.log(`✅ Success! Seeded ${userCount} users with posts.`);
}

main()
  .catch((e) => { console.error(e); process.exit(1); })
  .finally(async () => { await prisma.$disconnect(); });

3. Wire it into Package.json

Prisma has built-in support for seeding. Add this to your package.json so you can trigger the refresh with one command.

{
  "name": "my-express-api",
  "prisma": {
    "seed": "ts-node prisma/seed.ts"
  },
  "scripts": {
    "db:seed": "prisma db seed"
  }
}

4. Why This Wins

Scalability Testing: Want to see how your Express middleware handles 5,000 users? Just change userCount to 5000 and run the script.
Zero Manual Entry: No more "asdfghjkl" names in your UI. You get real names, real emails, and real paragraphs.
Sanitizing Dev: Every time you run npm run db:seed, you start with a predictable, clean state.

The Result in Express

Now, when you hit your GET /users endpoint, your UI will actually look like a real product:

app.get('/users', async (req, res) => {
  const users = await prisma.user.findMany({ include: { posts: true } });
  res.json(users); // Now returns a rich, realistic dataset!
});

Wrap Up

Setting up a seeder takes 5 minutes, but it saves hours of manual data entry over the life of a project. It’s the difference between guessing if your UI works and knowing it does.

Happy hacking! 🚀

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