Usage with JavaScript

MikroORM can be used with vanilla JavaScript using the defineEntity helper or EntitySchema. Both approaches provide full functionality without requiring TypeScript or decorators.

Using defineEntity

The defineEntity helper with property builders (p) is the recommended approach for defining entities in JavaScript:

./entities/Author.js

import { defineEntity, p } from '@mikro-orm/core';
import { Book } from './Book.js';

export const Author = defineEntity({
  name: 'Author',
  properties: {
    id: p.integer().primary(),
    name: p.string(),
    email: p.string().unique(),
    age: p.integer().nullable(),
    termsAccepted: p.boolean().default(false),
    born: p.date().nullable(),
    createdAt: p.datetime().onCreate(() => new Date()),
    updatedAt: p.datetime().onCreate(() => new Date()).onUpdate(() => new Date()),
    books: () => p.oneToMany(Book, { mappedBy: 'author' }),
    favouriteBook: () => p.manyToOne(Book).nullable(),
  },
});

./entities/Book.js

import { defineEntity, p } from '@mikro-orm/core';
import { Author } from './Author.js';
import { BookTag } from './BookTag.js';

export const Book = defineEntity({
  name: 'Book',
  properties: {
    id: p.integer().primary(),
    title: p.string(),
    author: () => p.manyToOne(Author),
    tags: () => p.manyToMany(BookTag),
  },
});

./entities/BookTag.js

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

export const BookTag = defineEntity({
  name: 'BookTag',
  properties: {
    id: p.integer().primary(),
    name: p.string(),
  },
});

Using defineEntity with a class

You can also use defineEntity with a class instead of just a name. This allows you to use new Author() to create instances and define custom methods on your entities:

./entities/Author.js

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

export class Author {
  id;
  name;
  email;

  getDisplayName() {
    return `${this.name} <${this.email}>`;
  }
}

export const AuthorSchema = defineEntity({
  class: Author,
  properties: {
    id: p.integer().primary(),
    name: p.string(),
    email: p.string().unique(),
  },
});

When using a class, the entity name is inferred from the class name. You can then use either the class or the schema when working with the ORM.

Registering entities

Register entities in your configuration:

import { MikroORM } from '@mikro-orm/sqlite';
import { Author } from './entities/Author.js';
import { Book } from './entities/Book.js';
import { BookTag } from './entities/BookTag.js';

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

Working with entities

Use em.create() to create entity instances:

const author = em.create(Author, {
  name: 'Jon Snow',
  email: 'jon@wall.st',
});

const book = em.create(Book, {
  title: 'My Life on the Wall',
  author,
});

await em.flush();

Using EntitySchema

As an alternative, you can use EntitySchema directly for more control:

./entities/Author.js

import { EntitySchema } from '@mikro-orm/core';

export const Author = new EntitySchema({
  name: 'Author',
  properties: {
    id: { type: 'number', primary: true },
    name: { type: 'string' },
    email: { type: 'string', unique: true },
    age: { type: 'number', nullable: true },
    termsAccepted: { type: 'boolean', default: false },
    born: { type: 'Date', nullable: true },
    createdAt: { type: 'Date', onCreate: () => new Date() },
    updatedAt: { type: 'Date', onCreate: () => new Date(), onUpdate: () => new Date() },
    books: { kind: '1:m', entity: () => Book, mappedBy: 'author' },
    favouriteBook: { kind: 'm:1', entity: () => Book, nullable: true },
  },
});

The kind parameter for relationships can be:

Value	Relationship
'1:1'	One-to-one
'm:1'	Many-to-one
'1:m'	One-to-many
'm:n'	Many-to-many
'embedded'	Embedded

Or you can use ReferenceKind enum, e.g. ReferenceKind.MANY_TO_ONE.

Read more about EntitySchema in the EntitySchema section.

Example repository

For a complete working example, see the Express JavaScript example app.