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, simply calling flush()
will run them inside a transaction.
You can also control the transaction boundaries manually via
em.transactional(cb)
.
const user = await em.findOne(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
await em.persistAndFlush(user);
MikroORM allows you to implement your domain/business logic directly in your entities. To maintain always valid entities, you can use constructors to mark required properties.
Once your entities are loaded, you can simply work with them and forget about persistence.
As you do not have to care about persistence, most of entity interactions can be synchronous.
When you have done all changes, you call em.flush()
. It will trigger computing of change
sets. Only entities that were changed will generate database queries, if there are no changes,
no transaction will be started.
This increases maintainability, flexibility and testability.
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's 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
).
- Clean and simple entity definition
- Identity Map
- Entity references
- Using entity constructors
- Collections
- Unit of Work
- Transactions
- Cascading persist and remove
- Using
QueryBuilder
- Preloading deeply nested structures via populate
- Property validation
- Lifecycle hooks
- Vanilla JS support
You 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
$ yarn add mikro-orm pg # for postgresql
$ yarn add mikro-orm sqlite # for sqlite
or
$ npm i -s mikro-orm mongodb # for mongo
$ npm i -s mikro-orm mysql2 # for mysql
$ npm i -s mikro-orm pg # for postgresql
$ npm i -s mikro-orm sqlite # for sqlite
Next you will need to enable support for decorators
in tsconfig.json
via:
"experimentalDecorators": 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',
clientUrl: '...', // defaults to 'mongodb://localhost:27017' for mongodb driver
autoFlush: false, // read more here: https://mikro-orm.io/unit-of-work/
});
console.log(orm.em); // access EntityManager via `em` property
There are more ways to configure your entities, take a look at installation page.
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
queryParser
orbodyParser
, 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):
./entities/Book.ts
@Entity()
export class Book {
@PrimaryKey()
_id: ObjectID;
@Property()
title: string;
@ManyToOne()
author: Author;
@ManyToMany({ entity: () => BookTag, inversedBy: 'books' })
tags = new Collection<BookTag>(this);
constructor(title: string, author: Author) {
this.title = title;
this.author = author;
}
}
export interface Book extends IEntity { }
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 EntityRepository
s.
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.