Installation

This tutorial builds a small event-sourced User model backed by PostgreSQL. You need Node.js 22 or newer, a NestJS 10 or 11 application, and a PostgreSQL database that your application can reach.

Install the packages

Install the core library, the PostgreSQL adapter, and the adapter's pg peer dependency:

pnpm add @event-nest/core @event-nest/postgresql pg

npm install @event-nest/core @event-nest/postgresql pg

yarn add @event-nest/core @event-nest/postgresql pg

Your application must also have these peer dependencies:

• @nestjs/common
• @nestjs/core
• reflect-metadata
• rxjs

A standard Nest application already includes them.

Prepare PostgreSQL

The tutorial uses a schema named event_nest. Create the database and schema before starting the application. Event Nest can create its tables, but it does not create the schema itself.

CREATE DATABASE event_nest;

Connect to that database, then create the schema:

CREATE SCHEMA IF NOT EXISTS event_nest;

Set the connection string in your environment:

export DATABASE_URL="postgresql://postgres:password@localhost:5432/event_nest"

Configure the adapter

Import EventNestPostgreSQLModule once in the application root:

import { EventNestPostgreSQLModule } from "@event-nest/postgresql";
import { Module } from "@nestjs/common";

@Module({
    imports: [
        EventNestPostgreSQLModule.forRoot({
            aggregatesTableName: "aggregates",
            connectionUri: process.env.DATABASE_URL ?? "postgresql://postgres:password@localhost:5432/event_nest",
            ensureTablesExist: true,
            eventsTableName: "events",
            schemaName: "event_nest"
        })
    ]
})
export class AppModule {}

forRoot() registers a global module and exports the event store under the EVENT_STORE injection token. The important options are:

Automatic initialization is convenient for this tutorial. For production, migrations are usually preferable because initialization errors are logged and the application must still be operated with a known schema.

Snapshots are intentionally disabled for this tutorial to keep things simple.

Check the connection

Start the Nest application once. With ensureTablesExist: true, the event_nest.aggregates and event_nest.events tables should exist after bootstrap. No row is written until an aggregate commits an event.

Next, define the events, aggregate, repository provider, and application service in Your First Aggregate .