mikro-orm

What is mikro-orm?

Mikro-ORM is a TypeScript ORM for Node.js based on Data Mapper, Unit of Work, and Identity Map patterns. It supports multiple databases including MongoDB, MySQL, PostgreSQL, SQLite, and MariaDB. It provides a powerful and flexible way to interact with your database using TypeScript and JavaScript.

What are mikro-orm's main functionalities?

Entity Definition

Defines an entity with properties that map to database columns. The `@Entity` decorator marks the class as a database entity, while `@PrimaryKey` and `@Property` decorators define the primary key and other properties respectively.

```typescript
import { Entity, PrimaryKey, Property } from 'mikro-orm';

@Entity()
class User {
  @PrimaryKey()
  id!: number;

  @Property()
  name!: string;

  @Property()
  email!: string;
}
```

CRUD Operations

Demonstrates basic Create, Read, Update, and Delete (CRUD) operations. The `persistAndFlush` method saves a new entity to the database, and the `find` method retrieves entities from the database.

```typescript
const user = new User();
user.name = 'John Doe';
user.email = '[e-mail]';
await orm.em.persistAndFlush(user);

const users = await orm.em.find(User, {});
console.log(users);
```

Query Builder

Shows how to use the query builder to construct and execute complex queries. The `createQueryBuilder` method creates a new query builder instance, and the `select` and `where` methods build the query.

```typescript
const qb = orm.em.createQueryBuilder(User);
const users = await qb.select('*').where({ name: 'John Doe' }).execute();
console.log(users);
```

Transactions

Illustrates how to perform operations within a transaction. The `transactional` method ensures that all operations within the callback are executed within a single transaction.

```typescript
await orm.em.transactional(async em => {
  const user = new User();
  user.name = 'Jane Doe';
  user.email = '[e-mail]';
  await em.persistAndFlush(user);
});
```

Other packages similar to mikro-orm

typeorm

TypeORM is another TypeScript ORM for Node.js that supports Active Record and Data Mapper patterns. It is highly popular and supports multiple databases. Compared to Mikro-ORM, TypeORM has a larger community and more extensive documentation, but Mikro-ORM offers a more modern and flexible API.

sequelize

Sequelize is a promise-based Node.js ORM for Postgres, MySQL, MariaDB, SQLite, and Microsoft SQL Server. It is known for its simplicity and ease of use. While Sequelize is more mature and has a larger user base, Mikro-ORM provides better TypeScript support and more advanced features like Unit of Work and Identity Map patterns.

objection

Objection.js is an SQL-friendly ORM for Node.js, built on top of the SQL query builder Knex.js. It aims to stay as close to the SQL syntax as possible while providing a powerful and flexible API. Compared to Mikro-ORM, Objection.js offers more control over raw SQL queries but lacks some of the higher-level abstractions and features provided by Mikro-ORM.

README

mikro-orm

Simple typescript mongo ORM for node.js based on data-mapper, unit-of-work and identity-map patterns.

Heavily inspired by doctrine.

Defining entity

import { BaseEntity, Entity, ManyToOne, Property } from 'mikro-orm';
import { Publisher } from './Publisher';
import { Author } from './Author';
import { BookRepository } from './BookRepository';

@Entity({ collection: 'books-table', customRepository: BookRepository })
export class Book extends BaseEntity {

  @Property()
  title: string;

  @ManyToOne({ entity: () => Author.name })
  author: Author;

  @ManyToOne({ entity: () => Publisher.name })
  publisher: Publisher;

  @Property()
  metaObject: object;

  @Property()
  metaArray: any[];

  @Property()
  metaArrayOfStrings: string[];

  constructor(title: string, author: Author) {
    super();
    this.title = title;
    this.author = author;
    this.metaObject = {};
    this.metaArray = [{test: 123, lol: true}];
    this.metaArrayOfStrings = ['test'];
  }

}

Installation

$ yarn add mikro-orm

or

$ npm install mikro-orm

Usage

import { MikroORM, Collection } from 'mikro-orm';
import { Author } from './entities/Author';
import { Published } from './entities/Published';
import { Book } from './entities/Book';

const orm = await MikroORM.init({
  entitiesDirs: ['entities'], // relative to `baseDir`
  dbName: 'my-db-name',
  baseDir: __dirname,
});

// use constructors in your entities
const author = new Author('Jon Snow', '[e-mail]');
author.born = new Date();

const publisher = new Publisher('7K publisher');

const book1 = new Book('My Life on The Wall, part 1', author);
book1.publisher = publisher;
const book2 = new Book('My Life on The Wall, part 2', author);
book2.publisher = publisher;
const book3 = new Book('My Life on The Wall, part 3', author);
book3.publisher = publisher;

await orm.em.persist(book1);
await orm.em.persist(book2);
await orm.em.persist(book3, true); // flush everything to database

const authorRepository = orm.em.getRepository<Author>(Author.name);
const jon = await authorRepository.findOne({ name: 'Jon Snow' }, ['books']);
const authors = await authorRepository.findAll(['books']);

// identity map in action
console.log(jon === authors[0]); // true

for (const author of authors) {
  console.log(author.name); // Jon Snow

  for (const book of author.books) {
    console.log(book.title); // initialized
    console.log(book.author.isInitialized()); // true
    console.log(book.author.id);
    console.log(book.author.name); // Jon Snow
    console.log(book.publisher); // just reference
    console.log(book.publisher.isInitialized()); // false
    console.log(book.publisher.id);
    console.log(book.publisher.name); // undefined
  }
}

// filtering and pagination
const booksRepository = orm.em.getRepository<Author>(Author.name);
const books = await booksRepository.find({ author: jon.id }, [], { title: -1 }, 2, 1);
console.log(books);

TODO

• cascade persist in collections
• immediate flush issue when persisting new entities with references
• aggregate support?
• improve populating in EM#find() method
• rehydrate and populate missing references when fetching already loaded entities from db
• support for string id (now we require object id) in EM/repositories

TODO docs

• custom repository
• cascading
• identity map
• lifecycle hooks