Effect

Existing database

Meet Drizzle

Get Started with Drizzle and Effect PostgreSQL in existing project

WARNING

This page explains concepts available on drizzle versions 1.0.0-beta.13 and higher.

Effect is only available for PostgreSQL right now and soon be implemented for all other dialects

On how to upgrade (read more here)

This guide assumes familiarity with:

Effect - Effect is a powerful TS library designed to help developers easily create complex, synchronous, and asynchronous programs. - read more
dotenv - package for managing environment variables - read here
tsx - package for running TypeScript files - read here
@effect/sql-pg - A PostgreSQL toolkit for Effect - read here

Basic file structure

This is the basic file structure of the project. In the src/db directory, we have table definition in schema.ts. In drizzle folder there are sql migration file and snapshots.

📦 <project root>
 ├ 📂 drizzle
 ├ 📂 src
 │   ├ 📂 db
 │   │  └ 📜 schema.ts
 │   └ 📜 index.ts
 ├ 📜 .env
 ├ 📜 drizzle.config.ts
 ├ 📜 package.json
 └ 📜 tsconfig.json

Step 1 - Install required packages

npm

yarn

pnpm

bun

npm i drizzle-orm effect @effect/sql-pg pg dotenv
npm i -D drizzle-kit tsx @types/pg

yarn add drizzle-orm effect @effect/sql-pg pg dotenv
yarn add -D drizzle-kit tsx @types/pg

pnpm add drizzle-orm effect @effect/sql-pg pg dotenv
pnpm add -D drizzle-kit tsx @types/pg

bun add drizzle-orm effect @effect/sql-pg pg dotenv
bun add -D drizzle-kit tsx @types/pg

Step 2 - Setup connection variables

Create a .env file in the root of your project and add your database connection variable:

DATABASE_URL=

tips

If you don’t have a PostgreSQL database yet and want to create one for testing, you can use our guide on how to set up PostgreSQL in Docker.

The PostgreSQL in Docker guide is available here. Go set it up, generate a database URL (explained in the guide), and come back for the next steps

Step 3 - Setup Drizzle config file

Drizzle config - a configuration file that is used by Drizzle Kit and contains all the information about your database connection, migration folder and schema files.

Create a drizzle.config.ts file in the root of your project and add the following content:

import 'dotenv/config';
import { defineConfig } from 'drizzle-kit';

export default defineConfig({
  out: './drizzle',
  schema: './src/db/schema.ts',
  dialect: 'postgresql',
  dbCredentials: {
    url: process.env.DATABASE_URL!,
  },
});

Step 4 - Introspect your database

Drizzle Kit provides a CLI command to introspect your database and generate a schema file with migrations. The schema file contains all the information about your database tables, columns, relations, and indices.

For example, you have such table in your database:

CREATE TABLE IF NOT EXISTS "users" (
	"id" integer PRIMARY KEY GENERATED ALWAYS AS IDENTITY (sequence name "users_id_seq" INCREMENT BY 1 MINVALUE 1 MAXVALUE 2147483647 START WITH 1 CACHE 1),
	"name" varchar(255) NOT NULL,
	"age" integer NOT NULL,
	"email" varchar(255) NOT NULL,
	CONSTRAINT "users_email_unique" UNIQUE("email")
);

Pull your database schema:

npx drizzle-kit pull --init

The result of introspection will be a schema.ts file, meta folder with snapshots of your database schema, sql file with the migration and relations.ts file for relational queries.

Here is an example of the generated schema.ts file:

// table schema generated by introspection
import { pgTable, unique, integer, varchar } from "drizzle-orm/pg-core"
import { sql } from "drizzle-orm"

export const users = pgTable("users", {
	id: integer().primaryKey().generatedAlwaysAsIdentity({ name: "users_id_seq", startWith: 1, increment: 1, minValue: 1, maxValue: 2147483647, cache: 1 }),
	name: varchar({ length: 255 }).notNull(),
	age: integer().notNull(),
	email: varchar({ length: 255 }).notNull(),
}, (table) => [
	unique("users_email_unique").on(table.email)
]);

Learn more about introspection in the documentation.

Step 5 - Transfer code to your actual schema file

We recommend transferring the generated code from drizzle/schema.ts and drizzle/relations.ts to the actual schema file. In this guide we transferred code to src/db/schema.ts. Generated files for schema and relations can be deleted. This way you can manage your schema in a more structured way.

 ├ 📂 drizzle
 │ ├ 📂 20242409125510_premium_mister_fear
 │ │ ├ 📜 snapshot.json
 │ │ └ 📜 migration.sql
 │ ├ 📜 relations.ts ────────┐
 │ └ 📜 schema.ts ───────────┤
 ├ 📂 src                    │ 
 │ ├ 📂 db                   │
 │ │ ├ 📜 relations.ts <─────┤
 │ │ └ 📜 schema.ts <────────┘
 │ └ 📜 index.ts         
 └ …

Step 6 - Connect Drizzle ORM to the database

Create a index.ts file in the src directory and initialize the connection:

import 'dotenv/config';
import * as PgDrizzle from 'drizzle-orm/effect-postgres';
import { PgClient } from '@effect/sql-pg';
import * as Effect from 'effect/Effect';
import * as Redacted from 'effect/Redacted';
import { types } from 'pg';

// Configure the PgClient layer with type parsers
const PgClientLive = PgClient.layer({
  url: Redacted.make(process.env.DATABASE_URL!),
  types: {
    getTypeParser: (typeId, format) => {
      // Return raw values for date/time types to let Drizzle handle parsing
      if ([1184, 1114, 1082, 1186, 1231, 1115, 1185, 1187, 1182].includes(typeId)) {
        return (val: any) => val;
      }
      return types.getTypeParser(typeId, format);
    },
  },
});

const program = Effect.gen(function*() {
  // Create the database with default services
  const db = yield* PgDrizzle.makeWithDefaults();

  // Your queries here...
});

// Run the program with the PgClient layer
Effect.runPromise(program.pipe(Effect.provide(PgClientLive)));

Step 7 - Query the database

import 'dotenv/config';
import * as PgDrizzle from 'drizzle-orm/effect-postgres';
import { PgClient } from '@effect/sql-pg';
import * as Effect from 'effect/Effect';
import * as Redacted from 'effect/Redacted';
import { types } from 'pg';
import { eq } from 'drizzle-orm';
import { usersTable } from './db/schema';

const PgClientLive = PgClient.layer({
  url: Redacted.make(process.env.DATABASE_URL!),
  types: {
    getTypeParser: (typeId, format) => {
      if ([1184, 1114, 1082, 1186, 1231, 1115, 1185, 1187, 1182].includes(typeId)) {
        return (val: any) => val;
      }
      return types.getTypeParser(typeId, format);
    },
  },
});

const program = Effect.gen(function*() {
  const db = yield* PgDrizzle.makeWithDefaults();

  const user: typeof usersTable.$inferInsert = {
    name: 'John',
    age: 30,
    email: '[email protected]',
  };

  yield* db.insert(usersTable).values(user);
  console.log('New user created!')

  const users = yield* db.select().from(usersTable);
  console.log('Getting all users from the database: ', users)
  /*
  const users: {
    id: number;
    name: string;
    age: number;
    email: string;
  }[]
  */

  yield* db
    .update(usersTable)
    .set({
      age: 31,
    })
    .where(eq(usersTable.email, user.email));
  console.log('User info updated!')

  yield* db.delete(usersTable).where(eq(usersTable.email, user.email));
  console.log('User deleted!')
});

Effect.runPromise(program.pipe(Effect.provide(PgClientLive)));

Step 8 - Run index.ts file

To run any TypeScript files, you have several options, but let’s stick with one: using tsx

You’ve already installed tsx, so we can run our queries now

Run index.ts script

npm

yarn

pnpm

bun

npx tsx src/index.ts

yarn tsx src/index.ts

pnpm tsx src/index.ts

bunx tsx src/index.ts

tips

We suggest using bun to run TypeScript files. With bun, such scripts can be executed without issues or additional settings, regardless of whether your project is configured with CommonJS (CJS), ECMAScript Modules (ESM), or any other module format. To run a script with bun, use the following command:

bun src/index.ts

If you don’t have bun installed, check the Bun installation docs

Step 9 - Update your table schema (optional)

If you want to update your table schema, you can do it in the schema.ts file. For example, let’s add a new column phone to the users_table:

import { pgTable, unique, integer, varchar } from "drizzle-orm/pg-core"
import { sql } from "drizzle-orm"

export const users = pgTable("users", {
	id: integer().primaryKey().generatedAlwaysAsIdentity({ name: "users_id_seq", startWith: 1, increment: 1, minValue: 1, maxValue: 2147483647, cache: 1 }),
	name: varchar({ length: 255 }).notNull(),
	age: integer().notNull(),
	email: varchar({ length: 255 }).notNull(),
  phone: varchar(),
}, (table) => [
	unique("users_email_unique").on(table.email)
]);

Step 10 - Applying changes to the database (optional)

You can directly apply changes to your database using the drizzle-kit push command. This is a convenient method for quickly testing new schema designs or modifications in a local development environment, allowing for rapid iterations without the need to manage migration files:

npx drizzle-kit push

Read more about the push command in documentation.

Tips

Alternatively, you can generate migrations using the drizzle-kit generate command and then apply them using the drizzle-kit migrate command:

Generate migrations:

npx drizzle-kit generate

Apply migrations:

npx drizzle-kit migrate

Read more about migration process in documentation.

Step 11 - Query the database with a new field (optional)

import 'dotenv/config';
import * as PgDrizzle from 'drizzle-orm/effect-postgres';
import { PgClient } from '@effect/sql-pg';
import * as Effect from 'effect/Effect';
import * as Redacted from 'effect/Redacted';
import { types } from 'pg';
import { eq } from 'drizzle-orm';
import { usersTable } from './db/schema';

const PgClientLive = PgClient.layer({
  url: Redacted.make(process.env.DATABASE_URL!),
  types: {
    getTypeParser: (typeId, format) => {
      if ([1184, 1114, 1082, 1186, 1231, 1115, 1185, 1187, 1182].includes(typeId)) {
        return (val: any) => val;
      }
      return types.getTypeParser(typeId, format);
    },
  },
});

const program = Effect.gen(function*() {
  const db = yield* PgDrizzle.makeWithDefaults();

  const user: typeof usersTable.$inferInsert = {
    name: 'John',
    age: 30,
    email: '[email protected]',
    phone: '123-456-7890',
  };

  yield* db.insert(usersTable).values(user);
  console.log('New user created!')

  const users = yield* db.select().from(usersTable);
  console.log('Getting all users from the database: ', users)
  /*
  const users: {
    id: number;
    name: string;
    age: number;
    email: string;
    phone: string | null;
  }[]
  */

  yield* db
    .update(usersTable)
    .set({
      age: 31,
    })
    .where(eq(usersTable.email, user.email));
  console.log('User info updated!')

  yield* db.delete(usersTable).where(eq(usersTable.email, user.email));
  console.log('User deleted!')
});

Effect.runPromise(program.pipe(Effect.provide(PgClientLive)));