MikroORM: Getting started

Read the full text on https://mikro-orm.io/docs/guide.

Introduction

MikroORM is a TypeScript ORM for Node.js based on Data Mapper, Unit of Work, and Identity Map patterns. In this guide, you will learn what those words mean, how to set up a simple API project, how to test it, and many more.

This Getting Started Guide was written as a step-by-step tutorial, accompanied by working StackBlitz examples and a GitHub repository with the final project. It will show you how to create a production-ready application from scratch, all the way down to a docker image you can deploy wherever you want.

The Stack

The goal of this guide is to show off the most important features of MikroORM as well as some of the more niche ones. It will walk you through creating a simple API for a blog, with the following technologies:

• MikroORM with SQLite driver
• Fastify as the web framework
• Vitest for testing
• ECMAScript modules
• JWT authentication
• reflection via ts-morph

What are we building?

We already mentioned what technologies will be used, and now more about the project. It will be a simple API for a blog, with authentication, publishing, and commenting. For that, we will use four regular entities: User, Article, Comment, and Tag. Later on, we will add one more entity, ArticleListing, a virtual entity represented by an SQL expression rather than a database table.

And the API routes description:

Method	URL	Description
POST	/user/sign-up	Register new user
POST	/user/sign-in	Login existing user
GET	/user/profile	Get your full profile info
PATCH	/user/profile	Modify your profile
POST	/article	Create new article
GET	/article	List existing articles
GET	/article/:slug	Get article detail
PATCH	/article/:slug	Modify existing article
DELETE	/article/:slug	Delete existing article
POST	/article/:slug/comment	Post comment for existing article

The code will be structured into self-contained modules: user, article, and common (for shared helpers).

The app will be using Node.js 20, TypeScript 5.2, and we will build it using a modern stack with ECMAScript modules enabled.

What will we cover

Here is (an incomplete) list of features you will try going through this guide.

• creating an app from scratch with TypeScript setup
• folder-based discovery, ts-morph reflection, ES modules
• request context management via middleware/fastify hook
• entity relations, advanced entity definition (e.g. lazy scalar properties)
• advanced type safety (e.g. OptionalProps, Reference wrapper and Loaded type)
• events, including advanced use cases like soft-delete via onFlush event
• basic testing via vitest
• custom repositories
• virtual entities
• serialization
• embeddables