Usage with MySQL, MariaDB, PostgreSQL or SQLite

To use mikro-orm with MySQL database, simply install the @mikro-orm/mysql dependency and set the type option to mysql when initializing ORM. Since v4 it is no longer needed to install the mysql2 package manually.

yarn add @mikro-orm/core @mikro-orm/mongodb     # for mongo
yarn add @mikro-orm/core @mikro-orm/mysql       # for mysql/mariadb
yarn add @mikro-orm/core @mikro-orm/mariadb     # for mysql/mariadb
yarn add @mikro-orm/core @mikro-orm/postgresql  # for postgresql
yarn add @mikro-orm/core @mikro-orm/sqlite      # for sqlite

or

npm i -s @mikro-orm/core @mikro-orm/mongodb     # for mongo
npm i -s @mikro-orm/core @mikro-orm/mysql       # for mysql/mariadb
npm i -s @mikro-orm/core @mikro-orm/mariadb     # for mysql/mariadb
npm i -s @mikro-orm/core @mikro-orm/postgresql  # for postgresql
npm i -s @mikro-orm/core @mikro-orm/sqlite      # for sqlite

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

To access driver specific methods like em.createQueryBuilder() we need to specify the driver type when calling MikroORM.init<D>(). Alternatively we can cast the orm.em to EntityManager exported from the driver package:

import { EntityManager } from '@mikro-orm/postgresql';
const em = orm.em as EntityManager;
const qb = em.createQueryBuilder(...);

import type { PostgreSqlDriver } from '@mikro-orm/postgresql'; // or any other SQL driver package

const orm = await MikroORM.init<PostgreSqlDriver>({
  entities: ['./dist/entities'], // path to your JS entities (dist), relative to `baseDir`
  dbName: 'my-db-name',
  type: 'postgresql',
});
console.log(orm.em); // access EntityManager via `em` property

Custom driver

If you want to use database that is not currently supported, you can implement your own driver. More information about how to create one can be found here. Then provide the driver class via driver configuration option:

import { MyCustomDriver } from './MyCustomDriver.ts';

const orm = await MikroORM.init<MyCustomDriver>({
  entities: [Author, Book, ...],
  dbName: 'my-db-name',
  driver: MyCustomDriver, // provide the class, not just its name
});

Schema

Currently you will need to maintain the database schema yourself. For initial dump, you can use SchemaGenerator helper.

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, 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);
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 res1 = await qb.execute();

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

QueryBuilder provides fluent interface with these methods:

QueryBuilder.select(fields: string | string[], distinct?: boolean): QueryBuilder;
QueryBuilder.insert(data: any): QueryBuilder;
QueryBuilder.update(data: any): QueryBuilder;
QueryBuilder.delete(cond: any): QueryBuilder;
QueryBuilder.count(fields: string | string[], distinct?: boolean): QueryBuilder;
QueryBuilder.join(field: string, alias?: string): QueryBuilder;
QueryBuilder.leftJoin(field: string, alias?: string): QueryBuilder;
QueryBuilder.where(cond: any, operator: '$and' | '$or'): QueryBuilder;
QueryBuilder.andWhere(cond: any): QueryBuilder;
QueryBuilder.orWhere(cond: any): QueryBuilder;
QueryBuilder.groupBy(fields: string | string[]): QueryBuilder;
QueryBuilder.having(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;
QueryBuilder.clone(): QueryBuilder;

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

Transactions

When you call em.flush(), all computed changes are queried inside a database transaction by default, so you do not have to handle transactions manually.

When you need to explicitly handle the transaction, you can use em.transactional(cb) to run callback in transaction. It will provide forked EntityManager as a parameter with 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.persistAndFlush(god);
});

LIKE Queries

SQL supports LIKE queries via native JS regular expressions:

const author1 = new Author2('Author 1', 'a1@example.com');
const author2 = new Author2('Author 2', 'a2@example.com');
const author3 = new Author2('Author 3', 'a3@example.com');
await orm.em.persistAndFlush([author1, author2, author3]);

// finds authors with email like '%exa%le.c_m'
const authors = await orm.em.find(Author2, { email: /exa.*le\.c.m$/ });
console.log(authors); // all 3 authors found

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:

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

Those methods execute native SQL queries generated via QueryBuilder based on entity metadata. 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>;

Additionally there is execute() method that supports executing raw SQL queries or QueryBuilder instances. To create QueryBuilder, you can use createQueryBuilder() factory method on both EntityManager and EntityRepository classes:

const qb = em.createQueryBuilder('Author');
qb.select('*').where({ id: { $in: [...] } });
const res = await em.getDriver().execute(qb);
console.log(res); // unprocessed result of underlying database driver

Using SQLite extensions

SQLite extensions like sqlean can add many useful features that are notably missing by default (e.g. regexp).

Once you've downloaded the binaries for the extensions you wish to use, they can be added by providing a pool.afterCreate handler in the SQLite initialization options. The handler should call loadExtension on the underlying database connection, passing the path to the extension binary:

const orm = await MikroORM.init<BetterSqliteDriver>({
  // ...
  pool: {
    afterCreate: (conn: any, done: any) => {
      conn.loadExtension('/.../sqlean-macos-arm64/sqlean');
      done(null, conn);
    },
  },
});