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mikro-orm

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Readme

mikro-orm

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

Heavily inspired by doctrine.

Installation & Usage

Fist 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

$ npm i -s mikro-orm mongodb # for mongo
$ npm i -s mikro-orm mysql2 # for mysql

Then call MikroORM.init as part of bootstrapping your app:

const orm = await MikroORM.init({
  entitiesDirs: ['entities'], // relative to `baseDir`
  dbName: 'my-db-name',
  clientUrl: '...', // defaults to 'mongodb://localhost:27017' for mongodb driver
  baseDir: __dirname, // defaults to `process.cwd()`
});
console.log(orm.em); // EntityManager

And do not forget to clear entity manager before each request if you do not want to store all loaded entities in memory:

const app = express();

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

Or ideally use the RequestContext helper to have dedicated identity maps for each request, as described here.

Now you can define your entities (in one of the entitiesDirs folders):

Defining entity

@Entity()
export class Book {

  @PrimaryKey()
  _id: ObjectID;

  @Property()
  createdAt = new Date();

  @Property({ onUpdate: () => new Date() })
  updatedAt = new Date();

  @Property()
  title: string;

  @ManyToOne({ entity: () => Author }) // you can pass the entity as class reference
  author: Author;

  @ManyToOne({ entity: () => Publisher.name }) // or you can pass the string name directly
  publisher: Publisher;

  constructor(title: string, author: Author) {
    this.title = title;
    this.author = author;
  }

}

export interface Book extends IEntity { }

You will need to extend Book's interface with IEntity or your entity must extend BaseEntity which does that for you. IEntity interface represents internal methods added to your entity's prototype via @Entity decorator.

With your entities set up, you can start using entity manager and repositories as described in following section. For more examples, take a look at tests/EntityManager.mongo.test.ts.

Persisting and cascading

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.persist([book1, book2, book3]);

// or one by one
await orm.em.persist(book1, false);
await orm.em.persist(book2, false);
await orm.em.persist(book3); // flush everything to database at once

Fetching entities with `EntityManager`

To fetch entities from database you can use find() and findOne() of EntityManager:

API:

EntityManager.getRepository<T extends IEntity>(entityName: string): EntityRepository<T>;
EntityManager.find<T extends IEntity>(entityName: string, where?: FilterQuery<T>, populate?: string[], orderBy?: { [k: string]: 1 | -1; }, limit?: number, offset?: number): Promise<T[]>;
EntityManager.findOne<T extends IEntity>(entityName: string, where: FilterQuery<T> | string, populate?: string[]): Promise<T>;
EntityManager.merge<T extends IEntity>(entityName: string, data: any): T;
EntityManager.getReference<T extends IEntity>(entityName: string, id: string): T;
EntityManager.remove(entityName: string, where: IEntity | any): Promise<number>;
EntityManager.removeEntity(entity: IEntity): Promise<number>;
EntityManager.count(entityName: string, where: any): Promise<number>;
EntityManager.persist(entity: IEntity | IEntity[], flush?: boolean): Promise<void>;
EntityManager.flush(): Promise<void>;
EntityManager.clear(): void;
EntityManager.canPopulate(entityName: string, property: string): boolean;

Example:

const author = orm.em.findOne(Author.name, '...id...');
const books = orm.em.find(Book.name, {});

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
  }
}

Using `EntityRepository` instead of `EntityManager`

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:

API:

EntityRepository.persist(entity: IEntity, flush?: boolean): Promise<void>;
EntityRepository.findOne(where: FilterQuery<IEntity> | string, populate?: string[]): Promise<IEntity>;
EntityRepository.find(where: FilterQuery<IEntity>, populate?: string[], orderBy?: { [k: string]: 1 | -1; }, limit?: number, offset?: number): Promise<IEntity[]>;
EntityRepository.findAll(populate?: string[], orderBy?: { [k: string]: 1 | -1; }, limit?: number, offset?: number): Promise<IEntity[]>;
EntityRepository.remove(where: IEntity | any): Promise<number>;
EntityRepository.flush(): Promise<void>;
EntityRepository.canPopulate(property: string): boolean;
EntityRepository.count(where?: any): Promise<number>;

Example:

const booksRepository = orm.em.getRepository<Book>(Book.name);

// with sorting, limit and offset parameters, populating author references
const books = await booksRepository.find({ author: '...' }, ['author'], { title: -1 }, 2, 1);
console.log(books); // Book[]

Custom repository

To use custom repository, just extend EntityRepository<T> class:

export class CustomAuthorRepository extends EntityRepository<Author> {

  // your custom methods...
  public findAndUpdate(...) {
    // ...
  }

}

And register your repository as @Entity decorator:

@Entity({ customRepository: () => CustomAuthorRepository })
export class Publisher {
  // ...
}

Note that we need to pass that repository reference inside a callback so we will not run into circular dependency issues when using entity references inside that repository.

Now you can access your custom repository via EntityManager.getRepository() method.

Core features

Identity Map

MikroORM uses identity map in background so you will always get the same instance of one entity.

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

If you want to clear this identity map cache, you can do so via EntityManager.clear() method:

orm.em.clear();

You should always keep unique identity map per each request. This basically means that you need to clone entity manager and use the clone in request context. There are two ways to achieve this:

Forking Entity Manager

With fork() method you can simply get clean entity manager with its own context and identity map:

const em = orm.em.fork();

`RequestContext` helper for DI containers

If you use dependency injection container like inversify or the one in nestjs framework, it can be hard to achieve this, because you usually want to access your repositories via DI container, but it will always provide you with the same instance, rather than new one for each request.

To solve this, you can use RequestContext helper, that will use node's async hooks in the background to isolate the request context. MikroORM will always use request specific (forked) entity manager if available, so all you need to do is to create new request context preferably in middle:

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

Entity references

Every single entity relation is mapped to an entity reference. Reference is an entity that has only its identifier. This reference is stored in identity map so you will get the same object reference when fetching the same document from database.

You can call await entity.init() to initialize the entity. This will trigger database call and populate itself, keeping the same reference in identity map.

const author = await orm.em.getReference('...id...');
console.log(author.id); // accessing the id will not trigger any db call
console.log(author.isInitialized()); // false
console.log(author.name); // undefined

await author.init(); // this will trigger db call
console.log(author.isInitialized()); // true
console.log(author.name); // defined

Using entity constructors

Internally, MikroORM never calls entity constructor, so you are free to use it as you wish. The constructor will be called only when you instantiate the class yourself via new operator, so it is a handy place to require your data when creating new entity.

For example following Book entity definition will always require to set title and author, but publisher will be optional:

@Entity({ collection: 'books-table' })
export class Book {

  @PrimaryKey()
  _id: ObjectID;

  @Property()
  title: string;

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

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

  @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 { }

Lifecycle hooks

You can use lifecycle hooks to run some code when entity gets persisted. You can mark any of entity methods with them, you can also mark multiple methods with same hook.

@BeforeCreate() and @BeforeUpdate() is fired right before we persist the entity in database
@AfterCreate() and @AfterUpdate() is fired right after the entity is updated in database and merged to identity map. Since this event entity will have reference to EntityManager and will be enabled to call entity.init() method (including all entity references and collections).
@BeforeDelete() is fired right before we delete the record from database. It is fired only when removing entity or entity reference, not when deleting records by query.
@AfterDelete() is fired right after the record gets deleted from database and it is unset from the identity map.

`ObjectID` and `string` duality (MongoDriver)

Every entity has both ObjectID and string id available, also all methods of EntityManager and EntityRepository supports querying by both of them.

const author = await orm.em.getReference('...id...');
console.log(author.id);  // returns '...id...'
console.log(author._id); // returns ObjectID('...id...')

// all of those will return the same results
const article = '...article id...'; // string id
const book = '...book id...'; // string id
const repo = orm.em.getRepository<Author>(Author.name);
const foo1 = await repo.find({ id: { $in: [article] }, favouriteBook: book });
const bar1 = await repo.find({ id: { $in: [new ObjectID(article)] }, favouriteBook: new ObjectID(book) });
const foo2 = await repo.find({ _id: { $in: [article] }, favouriteBook: book });
const bar2 = await repo.find({ _id: { $in: [new ObjectID(article)] }, favouriteBook: new ObjectID(book) });

Collections

OneToMany and ManyToMany collections are stored in a Collection wrapper. It implements iterator so you can use for of loop to iterate through it.

const author = orm.em.findOne(Author.name, '...', ['books']); // populating books collection

// or we could lazy load books collection later via `init()` method
await author.books.init();

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
}

// collection needs to be initialized before you can work with it
author.books.add(book);
console.log(author.books.contains(book)); // true
author.books.remove(book);
console.log(author.books.contains(book)); // false
author.books.add(book);
console.log(author.books.count()); // 1
author.books.removeAll();
console.log(author.books.contains(book)); // false
console.log(author.books.count()); // 0
console.log(author.books.getItems()); // Book[]
console.log(author.books.getIdentifiers()); // array of string | number
console.log(author.books.getIdentifiers('_id')); // array of ObjectID

`OneToMany` collections

OneToMany collections are inverse side of ManyToOne references, to which they need to point via fk attribute:

@Entity()
export class Book {

  @PrimaryKey()
  _id: ObjectID;

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

}

@Entity()
export class BookTag {

  @PrimaryKey()
  _id: ObjectID;

  @OneToMany({ entity: () => Book, fk: 'author' })
  books = new Collection<Book>(this);

}

`ManyToMany` collections

As opposed to SQL databases, with MongoDB we do not need to have join tables for ManyToMany relations. All references are stored as an array of ObjectIDs on owning entity.

Unidirectional

Unidirectional ManyToMany relations are defined only on one side, and marked explicitly as owner:

@ManyToMany({ entity: () => Book, owner: true })
books = new Collection<Book>(this);

Bidirectional

Bidirectional ManyToMany relations are defined on both sides, while one is owning side (where references are store), marked by inversedBy attribute pointing to the inverse side:

@ManyToMany({ entity: () => BookTag, inversedBy: 'books' })
tags = new Collection<BookTag>(this);

And on the inversed side we define it with mappedBy attribute poining back to the owner:

@ManyToMany({ entity: () => Book, mappedBy: 'tags' })
books = new Collection<Book>(this);

Updating entity values with `IEntity.assign()`

When you want to update entity based on user input, you will usually have just plain string ids of entity relations as user input. Normally you would need to use EntityManager.getReference() to create references from each id first, and then use those references to update entity relations:

const jon = new Author('Jon Snow', 'snow@wall.st');
const book = new Book('Book', jon);
book.author = orm.em.getReference<Author>(Author.name, '...id...');

Same result can be easily achieved with IEntity.assign():

book.assign({ 
  title: 'Better Book 1', 
  author: '...id...',
});
console.log(book.title); // 'Better Book 1'
console.log(book.author); // instance of Author with id: '...id...'
console.log(book.author.id); // '...id...'

Usage with MySQL

To use mikro-orm with MySQL database, do not forget to install mysql2 driver and provide MySqlDriver class when initializing ORM.

Then call MikroORM.init as part of bootstrapping your app:

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

Currently you will need to maintain the database schema yourself.

`ManyToMany` collections with pivot tables

As opposed to MongoDriver, in MySQL we use pivot tables to handle ManyToMany relations:

CREATE TABLE `publisher_to_test` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `publisher_id` int(11) DEFAULT NULL,
  `test_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

You can adjust the name of pivot table via pivotTable option in @ManyToMany decorator defined on owning side:

// for unidirectional
@ManyToMany({ entity: () => Test.name, owner: true, pivotTable: 'publisher2test' })
tests = new Collection<Test>(this);

// for bidirectional
@ManyToMany({ entity: () => BookTag, inversedBy: 'books', pivotTable: 'book2tag' })
tags = new Collection<BookTag>(this);

Using `QueryBuilder` to execute native SQL queries

When you need to execute some SQL query without all the ORM stuff involved, you can either compose the query yourself, or use the QueryBuilder helper to construct the query for you:

const qb = orm.em.createQueryBuilder(Author.name);
qb.update({ name: 'test 123', type: PublisherType.GLOBAL }).where({ id: 123, type: PublisherType.LOCAL });

console.log(qb.getQuery());
// 'UPDATE `publisher2` SET `name` = ?, `type` = ? WHERE `id` = ? AND `type` = ?'

console.log(qb.getParams());
// ['test 123', PublisherType.GLOBAL, 123, PublisherType.LOCAL]

// run the query
const driver = orm.em.getDriver<MySqlDriver>();
const res1 = await driver.execute(qb);

// or run query without using QueryBuilder
const res2 = await driver.execute('SELECT ? + ?', [1, 2]);

QueryBuilder provides fluent interface with these methods:

QueryBuilder.select(fields: string | string[]): QueryBuilder;
QueryBuilder.insert(data: any): QueryBuilder;
QueryBuilder.update(data: any): QueryBuilder;
QueryBuilder.delete(cond: any): QueryBuilder;
QueryBuilder.count(fields: string | string[]): QueryBuilder;
QueryBuilder.where(cond: any): QueryBuilder;
QueryBuilder.populate(populate: string[]): QueryBuilder;
QueryBuilder.limit(limit: number, offset?: number): QueryBuilder;
QueryBuilder.offset(offset: number): QueryBuilder;
QueryBuilder.getQuery(): string;
QueryBuilder.getParams(): any;

For more examples of how to work with QueryBuilder, take a look at QueryBuilder tests in tests/QueryBuilder.test.ts.

Transactions

MySQL driver provides basic support for transactions via begin/commit/rollback methods on both MySqlDriver and their shortcuts on EntityManager as well.

You can also use EntityManager.transactional(cb) helper to run callback in transaction. It will provide forked EntityManager as a parameter with clear clear isolated identity map - please use that to make changes.

// if an error occurs inside the callback, all db queries from inside the callback will be rolled back
await orm.em.transactional(async (em: EntityManager) => {
  const god = new Author('God', 'hello@heaven.god');
  await em.persist(god);
});

EntityManager.begin(): Promise<void>;
EntityManager.commit(): Promise<void>;
EntityManager.rollback(): Promise<void>;
EntityManager.transactional(cb: (em: EntityManager) => Promise<any>): Promise<any>;

Keep in mind transactions are supported only in MySQL driver currently.

Naming strategy in MySQL

MySqlDriver defaults to UnderscoreNamingStrategy, which means your all your database tables and columns will be lower-cased and words divided by underscored:

CREATE TABLE `author` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `created_at` datetime(3) DEFAULT NULL,
  `updated_at` datetime(3) DEFAULT NULL,
  `terms_accepted` tinyint(1) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `email` varchar(255) DEFAULT NULL,
  `born` datetime DEFAULT NULL,
  `favourite_book_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

You can also provide your own naming strategy, just implement NamingStrategy interface and provide your implementation when bootstrapping ORM:

class YourCustomNamingStrategy implements NamingStrategy {
  ...
}

const orm = await MikroORM.init({
  ...
  namingStrategy: YourCustomNamingStrategy,
  ...
});

Native collection methods

Sometimes you need to perform some bulk operation, or you just want to populate your database with initial fixtures. Using ORM for such operations can bring unnecessary boilerplate code. In this case, you can use one of nativeInsert/nativeUpdate/nativeDelete methods:

EntityManager.nativeInsert<T extends IEntity>(entityName: string, data: any): Promise<IPrimaryKey>;
EntityManager.nativeUpdate<T extends IEntity>(entityName: string, where: FilterQuery<T>, data: any): Promise<number>;
EntityManager.nativeDelete<T extends IEntity>(entityName: string, where: FilterQuery<T> | any): Promise<number>;

Those methods execute native driver methods like Mongo's insertOne/updateMany/deleteMany collection methods respectively. This is common interface for all drivers, so for MySQL driver, it will fire native SQL queries. Keep in mind that they do not hydrate results to entities, and they do not trigger lifecycle hooks.

They are also available as EntityRepository shortcuts:

EntityRepository.nativeInsert(data: any): Promise<IPrimaryKey>;
EntityRepository.nativeUpdate(where: FilterQuery<T>, data: any): Promise<number>;
EntityRepository.nativeDelete(where: FilterQuery<T> | any): Promise<number>;

There is also shortcut for calling aggregate method (available in MongoDriver only):

EntityManager.aggregate(entityName: string, pipeline: any[]): Promise<any[]>;
EntityRepository.aggregate(pipeline: any[]): Promise<any[]>;

Property validation

MirkoORM will validate your properties before actual persisting happens. It will try to fix wrong data types for you automatically. If automatic conversion fails, it will throw an error. You can enable strict mode to disable this feature and let ORM throw errors instead. Validation is triggered when persisting the entity.

// number instead of string will throw
const author = new Author('test', 'test');
author.assign({ name: 111, email: 222 });
await orm.em.persist(author); // throws "Validation error: trying to set Author.name of type 'string' to '111' of type 'number'"

// string date with unknown format will throw
author.assign(author, { name: '333', email: '444', born: 'asd' });
await orm.em.persist(author); // throws "Validation error: trying to set Author.born of type 'date' to 'asd' of type 'string'"

// string date with correct format will be auto-corrected
author.assign({ name: '333', email: '444', born: '2018-01-01' });
await orm.em.persist(author);
console.log(author.born).toBe(true); // instance of Date

// Date object will be ok
author.assign({ born: new Date() });
await orm.em.persist(author);
console.log(author.born).toBe(true); // instance of Date

// null will be ok
author.assign({ born: null });
await orm.em.persist(author);
console.log(author.born); // null

// string number with correct format will be auto-corrected
author.assign({ age: '21' });
await orm.em.persist(author);
console.log(author.age); // number 21

// string instead of number with will throw
author.assign({ age: 'asd' });
await orm.em.persist(author); // throws "Validation error: trying to set Author.age of type 'number' to 'asd' of type 'string'"
author.assign({ age: new Date() });
await orm.em.persist(author); // throws "Validation error: trying to set Author.age of type 'number' to '2019-01-17T21:14:23.875Z' of type 'date'"
author.assign({ age: false });
await orm.em.persist(author); // throws "Validation error: trying to set Author.age of type 'number' to 'false' of type 'boolean'"

TODO

cascade persist in collections
cascade remove references on other entities when deleting entity (e.g. from M:N collection)

mikro-orm

Package Exports

Readme

mikro-orm

Installation & Usage

Defining entity

Persisting and cascading

Fetching entities with EntityManager

Using EntityRepository instead of EntityManager

Custom repository

Core features

Identity Map

Forking Entity Manager

RequestContext helper for DI containers

Entity references

Using entity constructors

Lifecycle hooks

ObjectID and string duality (MongoDriver)

Collections

OneToMany collections

ManyToMany collections

Unidirectional

Bidirectional

Updating entity values with IEntity.assign()

Usage with MySQL

ManyToMany collections with pivot tables

Using QueryBuilder to execute native SQL queries

Transactions

Naming strategy in MySQL

Native collection methods

Property validation

TODO

Fetching entities with `EntityManager`

Using `EntityRepository` instead of `EntityManager`

`RequestContext` helper for DI containers

`ObjectID` and `string` duality (MongoDriver)

`OneToMany` collections

`ManyToMany` collections

Updating entity values with `IEntity.assign()`

`ManyToMany` collections with pivot tables

Using `QueryBuilder` to execute native SQL queries