@mikro-orm/core
Advanced tools
TypeScript ORM for Node.js based on Data Mapper, Unit of Work and Identity Map patterns. Supports MongoDB, MySQL, PostgreSQL and SQLite databases as well as usage with vanilla JavaScript.
@mikro-orm/core is an Object-Relational Mapper (ORM) for Node.js and TypeScript. It provides a powerful and flexible way to interact with databases using JavaScript/TypeScript objects. It supports multiple database drivers, including MySQL, PostgreSQL, SQLite, and MongoDB. The package offers features like entity management, query building, migrations, and more.
Entity Management
Entity management allows you to define and manage your database entities using decorators. In this example, a `User` entity is defined with `id`, `name`, and `email` properties.
const { Entity, PrimaryKey, Property } = require('@mikro-orm/core');
@Entity()
class User {
@PrimaryKey()
id;
@Property()
name;
@Property()
email;
}
const user = new User();
user.name = 'John Doe';
user.email = 'john.doe@example.com';Query Building
Query building allows you to perform database operations using a fluent API. In this example, a query is built to find all users with the name 'John Doe'.
const { MikroORM } = require('@mikro-orm/core');
async function main() {
const orm = await MikroORM.init({
entities: [User],
dbName: 'my-db-name',
type: 'postgresql',
});
const userRepository = orm.em.getRepository(User);
const users = await userRepository.find({ name: 'John Doe' });
console.log(users);
}
main();Migrations
Migrations allow you to manage database schema changes over time. In this example, a migration is created and then applied to the database.
const { MikroORM } = require('@mikro-orm/core');
async function main() {
const orm = await MikroORM.init({
entities: [User],
dbName: 'my-db-name',
type: 'postgresql',
});
const migrator = orm.getMigrator();
await migrator.createMigration(); // creates file Migration20201019195930.ts
await migrator.up(); // runs all pending migrations
}
main();TypeORM is another ORM for TypeScript and JavaScript (ES7, ES6, ES5). It supports multiple databases like MySQL, PostgreSQL, MariaDB, SQLite, and more. TypeORM is known for its active community and extensive documentation. Compared to @mikro-orm/core, TypeORM offers a similar feature set but with a different API and some additional features like Active Record pattern support.
Sequelize is a promise-based Node.js ORM for Postgres, MySQL, MariaDB, SQLite, and Microsoft SQL Server. It features solid transaction support, relations, eager and lazy loading, read replication, and more. Sequelize is widely used and has a large community. Compared to @mikro-orm/core, Sequelize is more mature and has broader database support but lacks some of the TypeScript-specific features.
Objection.js is an ORM for Node.js that aims to stay as close to the relational database as possible. It is built on top of the SQL query builder Knex.js. Objection.js is known for its simplicity and flexibility. Compared to @mikro-orm/core, Objection.js provides a more lightweight and less opinionated approach to ORM, making it suitable for developers who prefer more control over their SQL queries.
TypeScript ORM for Node.js based on Data Mapper, Unit of Work and Identity Map patterns. Supports MongoDB, MySQL, MariaDB, PostgreSQL and SQLite databases.
Heavily inspired by Doctrine and Nextras Orm.
You might be asking: What the hell is Unit of Work and why should I care about it?
Unit of Work maintains a list of objects (entities) affected by a business transaction and coordinates the writing out of changes. (Martin Fowler)
Identity Map ensures that each object (entity) gets loaded only once by keeping every loaded object in a map. Looks up objects using the map when referring to them. (Martin Fowler)
So what benefits does it bring to us?
First and most important implication of having Unit of Work is that it allows handling transactions automatically.
When you call em.flush(), all computed changes are queried inside a database
transaction (if supported by given driver). This means that you can control the boundaries
of transactions simply by calling em.persistLater() and once all your changes
are ready, calling flush() will run them inside a transaction.
You can also control the transaction boundaries manually via
em.transactional(cb).
const user = await em.findOneOrFail(User, 1);
user.email = 'foo@bar.com';
const car = new Car();
user.cars.add(car);
// thanks to bi-directional cascading we only need to persist user entity
// flushing will create a transaction, insert new car and update user with new email
// as user entity is managed, calling flush() is enough
await em.flush();
MikroORM allows you to implement your domain/business logic directly in the entities.
To maintain always valid entities, you can use constructors to mark required properties.
Let's define the User entity used in previous example:
@Entity()
export class User {
@PrimaryKey()
id!: number;
@Property()
name!: string;
@OneToOne()
address?: Address;
@ManyToMany()
cars = new Collection<Car>(this);
constructor(name: string) {
this.name = name;
}
}
Now to create new instance of the User entity, we are forced to provide the name:
const user = new User('John Doe'); // name is required to create new user instance
user.address = new Address('10 Downing Street'); // address is optional
Once your entities are loaded, make a number of synchronous actions on your entities,
then call em.flush(). This will trigger computing of change sets. Only entities
(and properties) that were changed will generate database queries, if there are no changes,
no transaction will be started.
const user = await em.findOneOrFail(User, 1, ['cars', 'address']);
user.title = 'Mr.';
user.address.street = '10 Downing Street'; // address is 1:1 relation of Address entity
user.cars.getItems().forEach(car => car.forSale = true); // cars is 1:m collection of Car entities
const car = new Car('VW');
user.cars.add(car);
// now we can flush all changes done to managed entities
await em.flush();
em.flush() will then execute these queries from the example above:
begin;
update user set title = 'Mr.' where id = 1;
update user_address set street = '10 Downing Street' where id = 123;
update car set for_sale = true where id = 1;
update car set for_sale = true where id = 2;
update car set for_sale = true where id = 3;
insert into car (brand, owner) values ('VW', 1);
commit;
Thanks to Identity Map, you will always have only one instance of given entity in one context.
This allows for some optimizations (skipping loading of already loaded entities), as well as
comparison by identity (ent1 === ent2).
MikroORM v3 documentation, included in this repo in the root directory, is built with Jekyll and publicly hosted on GitHub Pages at https://mikro-orm.io.
There is also auto-generated CHANGELOG.md file based on commit messages
(via semantic-release).
You can browse MikroORM v2 docs at https://mikro-orm.io/docs/2.7/installation.
To upgrade to v3, please see the upgrading guide.
QueryBuilderYou can find example integrations for some popular frameworks in the mikro-orm-examples repository:
First install the module via yarn or npm and do not forget to install the database driver as well:
$ yarn add mikro-orm mongodb # for mongo
$ yarn add mikro-orm mysql2 # for mysql/mariadb
$ yarn add mikro-orm mariadb # for mysql/mariadb
$ yarn add mikro-orm pg # for postgresql
$ yarn add mikro-orm sqlite3 # for sqlite
or
$ npm i -s mikro-orm mongodb # for mongo
$ npm i -s mikro-orm mysql2 # for mysql/mariadb
$ npm i -s mikro-orm mariadb # for mysql/mariadb
$ npm i -s mikro-orm pg # for postgresql
$ npm i -s mikro-orm sqlite3 # for sqlite
Next you will need to enable support for decorators
as well as esModuleInterop in tsconfig.json via:
"experimentalDecorators": true,
"esModuleInterop": true
Then call MikroORM.init as part of bootstrapping your app:
const orm = await MikroORM.init({
entitiesDirs: ['./dist/entities'], // path to your JS entities (dist), relative to `baseDir`
dbName: 'my-db-name',
type: 'mongo',
clientUrl: '...', // defaults to 'mongodb://localhost:27017' for mongodb driver
});
console.log(orm.em); // access EntityManager via `em` property
There are more ways to configure your entities, take a look at installation page.
Read more about all the possible configuration options in Advanced Configuration section.
Then you will need to fork entity manager for each request so their
identity maps will not collide.
To do so, use the RequestContext helper:
const app = express();
app.use((req, res, next) => {
RequestContext.create(orm.em, next);
});
You should register this middleware as the last one just before request handlers and before any of your custom middleware that is using the ORM. There might be issues when you register it before request processing middleware like
queryParserorbodyParser, so definitely register the context after them.
More info about RequestContext is described here.
Now you can start defining your entities (in one of the entitiesDirs folders). This is how
simple entity can look like in mongo driver:
./entities/MongoBook.ts
@Entity()
export class MongoBook {
@PrimaryKey()
_id: ObjectID;
@SerializedPrimaryKey()
id: string;
@Property()
title: string;
@ManyToOne()
author: Author;
@ManyToMany()
tags = new Collection<BookTag>(this);
constructor(title: string, author: Author) {
this.title = title;
this.author = author;
}
}
For SQL drivers, you can use id: number PK:
./entities/SqlBook.ts
@Entity()
export class SqlBook {
@PrimaryKey()
id: number;
}
Or if you want to use UUID primary keys:
./entities/UuidBook.ts
import { v4 } from 'uuid';
@Entity()
export class UuidBook {
@PrimaryKey()
uuid = v4();
}
More information can be found in defining entities section in docs.
When you have your entities defined, you can start using ORM either via EntityManager
or via EntityRepositorys.
To save entity state to database, you need to persist it. Persist takes care or deciding
whether to use insert or update and computes appropriate change-set. Entity references
that are not persisted yet (does not have identifier) will be cascade persisted automatically.
// use constructors in your entities for required parameters
const author = new Author('Jon Snow', 'snow@wall.st');
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;
// just persist books, author and publisher will be automatically cascade persisted
await orm.em.persistAndFlush([book1, book2, book3]);
To fetch entities from database you can use find() and findOne() of EntityManager:
const authors = orm.em.find(Author, {});
for (const author of authors) {
console.log(author); // instance of Author entity
console.log(author.name); // Jon Snow
for (const book of author.books) { // iterating books collection
console.log(book); // instance of Book entity
console.log(book.title); // My Life on The Wall, part 1/2/3
}
}
More convenient way of fetching entities from database is by using EntityRepository, that
carries the entity name so you do not have to pass it to every find and findOne calls:
const booksRepository = orm.em.getRepository(Book);
// with sorting, limit and offset parameters, populating author references
const books = await booksRepository.find({ author: '...' }, ['author'], { title: QueryOrder.DESC }, 2, 1);
// or with options object
const books = await booksRepository.find({ author: '...' }, {
populate: ['author'],
limit: 1,
offset: 2,
sort: { title: QueryOrder.DESC },
});
console.log(books); // Book[]
Take a look at docs about working with EntityManager
or using EntityRepository instead.
Contributions, issues and feature requests are welcome. Please read CONTRIBUTING.md for details on the process for submitting pull requests to us.
👤 Martin Adámek
See also the list of contributors who participated in this project.
Please ⭐️ this repository if this project helped you!
Copyright © 2018 Martin Adámek.
This project is licensed under the MIT License - see the LICENSE file for details.
FAQs
TypeScript ORM for Node.js based on Data Mapper, Unit of Work and Identity Map patterns. Supports MongoDB, MySQL, PostgreSQL and SQLite databases as well as usage with vanilla JavaScript.
The npm package @mikro-orm/core receives a total of 199,388 weekly downloads. As such, @mikro-orm/core popularity was classified as popular.
We found that @mikro-orm/core demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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