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Version: 7.0 (next)

Separating Concerns using Embeddables

Support for embeddables was added in version 4.0

Embeddables are classes which are not entities themselves, but are embedded in entities and can also be queried. You'll mostly want to use them to reduce duplication or separating concerns. Value objects such as date range or address are the primary use case for this feature.

Embeddables needs to be discovered just like regular entities, don't forget to add them to the list of entities when initializing the ORM.

Embeddables can contain properties with basic @Property() mapping, nested @Embedded() properties or arrays of @Embedded() properties. From version 5.0 you can also use @ManyToOne() properties.

For the purposes of this tutorial, let's assume that you have a User class in your application, and you would like to store an address in the User class. The Address class will be modeled as an embeddable instead of simply adding the respective columns to the User class.

import { type InferEntity, defineEntity, p } from '@mikro-orm/core';

export const User = defineEntity({
  name: 'User',
  properties: {
    id: p.integer().primary(),
    address: () => p.embedded(Address),
  },
});

export type IUser = InferEntity<typeof User>;

export const Address = defineEntity({
  name: 'Address',
  embeddable: true,
  properties: {
    street: p.string(),
    postalCode: p.string(),
    city: p.string(),
    country: p.string(),
  },
});

export type IAddress = InferEntity<typeof Address>;

When using ReflectMetadataProvider, you might need to provide the class in decorator options: @Embedded(() => Address) or @Embedded({ entity: () => Address }).

In terms of your database schema, MikroORM will automatically inline all columns from the Address class into the table of the User class, just as if you had declared them directly there.

Initializing embeddables​

In case all fields in the embeddable are nullable, you might want to initialize the embeddable, to avoid getting a null value instead of the embedded object.

./entities/User.ts
const User = defineEntity({
  name: 'User',
  properties: {
    id: p.integer().primary(),
    address: () => p.embedded(Address)
      .onCreate(() => new Address()),
  },
});

Column Prefixing​

By default, MikroORM names your columns by prefixing them, using the value object name.

Following the example above, your columns would be named as address_street, address_postal_code...

You can change this behaviour to meet your needs by changing the prefix attribute in the @Embedded() notation.

The following example shows you how to set your prefix to myPrefix_:

./entities/User.ts
const User = defineEntity({
  name: 'User',
  properties: {
    id: p.integer().primary(),
    address: () => p.embedded(Address).prefix('myPrefix_')
  },
});

You can also decide more precisely how the column name is determined with an explicit prefix. With the example below:

  • relative mode (default) concatenates the prefix with its parent's prefix (if any), naming them contact_addr2_city, contact_addr2_street, ...
  • absolute mode sets the prefix at the beginning of the column, naming them addr_city, addr_street, ...
./entities/User.ts
export const Contact = defineEntity({
  name: 'Contact',
  embeddable: true,
  properties: {
    address: () => p.embedded(Address).prefix('addr_').prefixMode('absolute'),
    address2: () => p.embedded(Address).prefix('addr2_').prefixMode('relative'),
  },
});

export type IContact = InferEntity<typeof Contact>;

export const User = defineEntity({
  name: 'User',
  properties: {
    id: p.integer().primary(),
    contact: () => p.embedded(Contact),
  },
});

export type IUser = InferEntity<typeof User>;

The default behavior can be overridden in the ORM configuration:

MikroORM.init({
  embeddables: {
    prefixMode: 'absolute', // defaults to `true`
  }, 
})

To have MikroORM drop the prefix and use the value object's property name directly, set prefix: false:

./entities/User.ts
const User = defineEntity({
  name: 'User',
  properties: {
    id: p.integer().primary(),
    address: () => p.embedded(Address).prefix(false),
  },
});

Storing embeddables as objects​

You can also store the embeddable as an object instead of inlining its properties to the owning entity.

./entities/User.ts
const User = defineEntity({
  name: 'User',
  properties: {
    id: p.integer().primary(),
    address: () => p.embedded(Address).object(),
  },
});

In SQL drivers, this will use a JSON column to store the value.

Only MySQL and PostgreSQL drivers support searching by JSON properties currently.

This part of documentation is highly inspired by doctrine tutorial as the behaviour here is pretty much the same.

Array of embeddables​

Embedded arrays are always stored as JSON. It is possible to use them inside nested embeddables.

./entities/User.ts
const User = defineEntity({
  name: 'User',
  properties: {
    id: p.integer().primary(),
    addresses: () => p.embedded(Address).array().onCreate(() => []),
  },
});

Nested embeddables​

You can also nest embeddables, both in inline mode and object mode:

./entities/User.ts
export const User = defineEntity({
  name: 'User',
  properties: {
    id: p.integer().primary(),
    name: p.string(),
    address: () => p.embedded(Address),
  },
});

export type IUser = InferEntity<typeof User>;

export const Profile = defineEntity({
  name: 'Profile',
  embeddable: true,
  properties: {
    username: p.string(),
    identity: () => p.embedded(Identity),
  },
});

export type IProfile = InferEntity<typeof Profile>;

export const Identity = defineEntity({
  name: 'Identity',
  embeddable: true,
  properties: {
    email: p.string(),
  },
});

export type IIdentity = InferEntity<typeof Identity>;

Polymorphic embeddables​

It is also possible to use polymorphic embeddables. This means you can define multiple classes for a single embedded property and the right one will be used based on the discriminator column, similar to how single table inheritance work.

import { defineEntity, p, type InferEntity } from '@mikro-orm/core';

export enum AnimalType {
  CAT,
  DOG,
}

export const Animal = defineEntity({
  name: 'Animal',
  embeddable: true,
  abstract: true,
  discriminatorColumn: 'type',
  properties: {
    type: p.enum(() => AnimalType),
    name: p.string(),
  },
});

export const Cat = defineEntity({
  name: 'Cat',
  embeddable: true,
  extends: Animal,
  discriminatorValue: AnimalType.CAT,
  properties: {
    canMeow: p.boolean().nullable(),
  },
});

export const Dog = defineEntity({
  name: 'Dog',
  embeddable: true,
  extends: Animal,
  discriminatorValue: AnimalType.DOG,
  properties: {
    canBark: p.boolean().nullable(),
  },
});

export const Owner = defineEntity({
  name: 'Owner',
  properties: {
    id: p.integer().primary(),
    name: p.string(),
    pet: () => p.embedded([Cat, Dog]),
  },
});

export type Cat = InferEntity<typeof Cat>;
export type Dog = InferEntity<typeof Dog>;
export type Owner = InferEntity<typeof Owner>;