MikroORM

TypeScript ORM for Node.js based on Data Mapper, Unit of Work and Identity Map patterns. Supports MongoDB, MySQL, MariaDB, PostgreSQL (including CockroachDB and PGlite), SQLite (including libSQL), MSSQL and Oracle databases.

Heavily inspired by Doctrine and Hibernate.

Quick Start

Install a driver package for your database:

npm install @mikro-orm/postgresql   # PostgreSQL
npm install @mikro-orm/pglite       # PGlite (embedded PostgreSQL in WASM)
npm install @mikro-orm/mysql        # MySQL
npm install @mikro-orm/mariadb      # MariaDB
npm install @mikro-orm/sqlite       # SQLite
npm install @mikro-orm/libsql       # libSQL / Turso
npm install @mikro-orm/sql-js       # sql.js (in-memory SQLite in WASM)
npm install @mikro-orm/mongodb      # MongoDB
npm install @mikro-orm/mssql        # MS SQL Server
npm install @mikro-orm/oracledb     # Oracle

If you use additional packages like @mikro-orm/cli, @mikro-orm/migrations, or @mikro-orm/entity-generator, install @mikro-orm/core explicitly as well. See the quick start guide for details.

Define Entities

The recommended way to define entities is using defineEntity with setClass:

import { defineEntity, p, MikroORM } from '@mikro-orm/postgresql';

const AuthorSchema = defineEntity({
  name: 'Author',
  properties: {
    id: p.integer().primary(),
    name: p.string(),
    email: p.string(),
    born: p.datetime().nullable(),
    books: () => p.oneToMany(Book).mappedBy('author'),
  },
});

export class Author extends AuthorSchema.class {}
AuthorSchema.setClass(Author);

const BookSchema = defineEntity({
  name: 'Book',
  properties: {
    id: p.integer().primary(),
    title: p.string(),
    author: () => p.manyToOne(Author).inversedBy('books'),
  },
});

export class Book extends BookSchema.class {}
BookSchema.setClass(Book);

You can also define entities using decorators or EntitySchema. See the defining entities guide for all options.

Initialize and Use

import { MikroORM, RequestContext } from '@mikro-orm/postgresql';

const orm = await MikroORM.init({
  entities: [Author, Book],
  dbName: 'my-db',
});

// Create new entities
const author = orm.em.create(Author, {
  name: 'Jon Snow',
  email: '[email protected]',
});
const book = orm.em.create(Book, {
  title: 'My Life on The Wall',
  author,
});

// Flush persists all tracked changes in a single transaction
await orm.em.flush();

Querying

// Find with relations
const authors = await orm.em.findAll(Author, {
  populate: ['books'],
  orderBy: { name: 'asc' },
});

// Type-safe QueryBuilder
const qb = orm.em.createQueryBuilder(Author);
const result = await qb
  .select('*')
  .where({ books: { title: { $like: '%Wall%' } } })
  .getResult();

Request Context

In web applications, use RequestContext to isolate the identity map per request:

const app = express();

app.use((req, res, next) => {
  RequestContext.create(orm.em, next);
});

More info about RequestContext is described here.

Unit of Work

Unit of Work maintains a list of objects (entities) affected by a business transaction and coordinates the writing out of changes. (Martin Fowler)

When you call em.flush(), all computed changes are queried inside a database transaction. This means you can control transaction boundaries simply by making changes to your entities and calling flush() when ready.

const author = await em.findOneOrFail(Author, 1, {
  populate: ['books'],
});
author.name = 'Jon Snow II';
author.books.getItems().forEach(book => book.title += ' (2nd ed.)');
author.books.add(orm.em.create(Book, { title: 'New Book', author }));

// Flush computes change sets and executes them in a single transaction
await em.flush();

The above flush will execute:

begin;
update "author" set "name" = 'Jon Snow II' where "id" = 1;
update "book"
  set "title" = case
    when ("id" = 1) then 'My Life on The Wall (2nd ed.)'
    when ("id" = 2) then 'Another Book (2nd ed.)'
    else "title" end
  where "id" in (1, 2);
insert into "book" ("title", "author_id") values ('New Book', 1);
commit;

This is the beginning of the README. Read the rest at the original. Read the full README ↗