PostgreSQL

PostgreSQL is a widely used open-source relational database. In this guide, you will learn how to add Prisma ORM to an existing TypeScript project, connect it to PostgreSQL, introspect your existing database schema, and start querying with type-safe Prisma Client.

Navigate to your existing project directory and install the required dependencies:

bun add prisma@prev @types/node @types/pg --dev

bun add @prisma/client@7 @prisma/adapter-pg pg dotenv

pnpm add prisma@prev @types/node @types/pg --save-dev
pnpm add @prisma/client@7 @prisma/adapter-pg pg dotenv

yarn add prisma@prev @types/node @types/pg --dev
yarn add @prisma/client@7 @prisma/adapter-pg pg dotenv

npm install prisma@prev @types/node @types/pg --save-dev
npm install @prisma/client@7 @prisma/adapter-pg pg dotenv

Here's what each package does:

• prisma - The Prisma CLI for running commands like prisma init, prisma db pull, and prisma generate
• @prisma/client - The Prisma Client library for querying your database
• @prisma/adapter-pg - The node-postgres driver adapter that connects Prisma Client to your database
• pg - The node-postgres database driver
• @types/pg - TypeScript type definitions for node-postgres
• dotenv - Loads environment variables from your .env file

Set up your Prisma ORM project by creating your Prisma Schema file with the following command:

bunx --bun prisma init --datasource-provider postgresql --output ../generated/prisma

pnpm prisma init --datasource-provider postgresql --output ../generated/prisma

yarn prisma init --datasource-provider postgresql --output ../generated/prisma

npx prisma init --datasource-provider postgresql --output ../generated/prisma

This command does a few things:

• Creates a prisma/ directory with a schema.prisma file containing your database connection configuration
• Creates a .env file in the root directory for environment variables
• Creates a prisma7.config.ts file for Prisma configuration

The generated prisma7.config.ts file looks like this:

// This file was generated by Prisma, and assumes you have installed the following:

// npm install --save-dev prisma dotenv

import "dotenv/config";

import { defineConfig } from "prisma/config";

export default defineConfig({

  schema: "prisma/schema.prisma",

  migrations: {

    path: "prisma/migrations",

  },

  datasource: {

    url: process.env["DATABASE_URL"],

  },

});

The generated schema uses the ESM-first prisma-client generator with a custom output path:

generator client {

  provider = "prisma-client"

  output   = "../generated/prisma"

}

datasource db {

  provider = "postgresql"

}

Update the .env file with your PostgreSQL connection URL:

DATABASE_URL="postgresql://user:password@localhost:5432/mydb?schema=public"

The format of the connection URL for PostgreSQL looks as follows:

postgresql://USER:PASSWORD@HOST:PORT/DATABASE?schema=SCHEMA

Run the following command to introspect your existing database:

• bun
• pnpm
• yarn
• npm

bunx prisma db pull

pnpm prisma db pull

yarn prisma db pull

npx prisma db pull

This command reads the DATABASE_URL environment variable, connects to your database, and introspects the database schema. It then translates the database schema from SQL into a data model in your Prisma schema.

After introspection, your Prisma schema will contain models that represent your existing database tables.

This command reads the DATABASE_URL environment variable, connects to your database, and introspects the database schema. It then translates the database schema from SQL into a data model in your Prisma schema.

After introspection, your Prisma schema will contain models that represent your existing database tables.

To use Prisma Migrate with your existing database, you need to baseline your database.

First, create a migrations directory:

mkdir -p prisma/migrations/0_init

Next, generate the migration file with prisma migrate diff:

bunx prisma migrate diff --from-empty --to-schema prisma/schema.prisma --script > prisma/migrations/0_init/migration.sql

pnpm prisma migrate diff --from-empty --to-schema prisma/schema.prisma --script > prisma/migrations/0_init/migration.sql

yarn prisma migrate diff --from-empty --to-schema prisma/schema.prisma --script > prisma/migrations/0_init/migration.sql

npx prisma migrate diff --from-empty --to-schema prisma/schema.prisma --script > prisma/migrations/0_init/migration.sql

Review the generated migration file to ensure it matches your database schema.

Then, mark the migration as applied:

bunx prisma migrate resolve --applied 0_init

pnpm prisma migrate resolve --applied 0_init

yarn prisma migrate resolve --applied 0_init

npx prisma migrate resolve --applied 0_init

You now have a baseline for your current database schema.

Generate Prisma Client based on your introspected schema:

bunx prisma generate

pnpm prisma generate

yarn prisma generate

npx prisma generate

This creates a type-safe Prisma Client tailored to your database schema in the generated/prisma directory.

Create a utility file to instantiate Prisma Client. You need to pass an instance of the Prisma ORM driver adapter adapter to the PrismaClient constructor:

import "dotenv/config";

import { PrismaPg } from "@prisma/adapter-pg";

import { PrismaClient } from "../generated/prisma/client";

const connectionString = `${process.env.DATABASE_URL}`;

const adapter = new PrismaPg({ connectionString });

const prisma = new PrismaClient({ adapter });

export { prisma };

Now you can use Prisma Client to query your database. Create a script.ts file:

import { prisma } from "./lib/prisma";

async function main() {

  // Example: Fetch all records from a table

  // Replace 'user' with your actual model name

  const allUsers = await prisma.user.findMany();

  console.log("All users:", JSON.stringify(allUsers, null, 2));

}

main()

  .then(async () => {

    await prisma.$disconnect();

  })

  .catch(async (e) => {

    console.error(e);

    await prisma.$disconnect();

    process.exit(1);

  });

Run the script:

bunx tsx script.ts

pnpm dlx tsx script.ts

yarn dlx tsx script.ts

npx tsx script.ts

To make changes to your database schema:

Update your Prisma schema file to reflect the changes you want to make to your database schema. For example, add a new model:

model Post { 

  id        Int      @id @default(autoincrement()) 

  title     String

  content   String?

  published Boolean  @default(false) 

  authorId  Int

  author    User     @relation(fields: [authorId], references: [id]) 

} 

model User { 

  id    Int    @id @default(autoincrement()) 

  email String @unique

  name  String?

  posts Post[]

} 

bunx prisma migrate dev --name your_migration_name

pnpm prisma migrate dev --name your_migration_name

yarn prisma migrate dev --name your_migration_name

npx prisma migrate dev --name your_migration_name

This command will:

• Create a new SQL migration file
• Apply the migration to your database
• Regenerate Prisma Client

npx prisma studio

Prisma ORM is set up. These are the pages you are most likely to need next:

• Learn more about Prisma Client: Explore the Prisma Client API for advanced querying, filtering, and relations
• Database migrations: Learn about Prisma Migrate for evolving your database schema
• Performance optimization: Discover query optimization techniques
• Build a full application: Check out our framework guides to integrate Prisma ORM with Next.js, Express, and more
• Join the community: Connect with other developers on Discord

• PostgreSQL database connector
• Prisma Config reference
• Database introspection
• Prisma Migrate