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Defining Entities via EntitySchema

With EntitySchema helper we define the schema programmatically.

./entities/Book.ts
export interface Book extends CustomBaseEntity {
  title: string;
  author: Author;
  publisher: Publisher;
  tags: Collection<BookTag>;
}

// The second type argument is optional, and should be used only with custom
// base entities, not with the `BaseEntity` class exported from `@mikro-orm/core`.
export const schema = new EntitySchema<Book, CustomBaseEntity>({
  // name should be used only with interfaces
  name: 'Book',
  // if we use actual class, we need this instead:
  // class: Book,
  extends: CustomBaseEntitySchema, // only if we extend custom base entity
  properties: {
    title: { type: 'string' },
    author: { kind: 'm:1', entity: 'Author', inversedBy: 'books' },
    publisher: { kind: 'm:1', entity: 'Publisher', inversedBy: 'books' },
    tags: { kind: 'm:n', entity: 'BookTag', inversedBy: 'books', fixedOrder: true },
  },
});

When creating new entity instances, you will need to use em.create() method that will create instance of internally created class.

// instance of internal Author class
const author = em.create<Author>('Author', { name: 'name', email: 'email' });
await em.flush();

Using this approach, metadata caching is automatically disabled as it is not needed.

Using custom entity classes​

You can optionally use custom class for entity instances.

./entities/Author.ts
export class Author extends CustomBaseEntity {
  name: string;
  email: string;
  age?: number;
  termsAccepted?: boolean;
  identities?: string[];
  born?: string;
  books = new Collection<Book>(this);
  favouriteBook?: Book;
  version?: number;

  constructor(name: string, email: string) {
    super();
    this.name = name;
    this.email = email;
  }
}

export const schema = new EntitySchema<Author, CustomBaseEntity>({
  class: Author,
  extends: CustomBaseEntitySchema,
  properties: {
    name: { type: 'string' },
    email: { type: 'string', unique: true },
    age: { type: 'number', nullable: true },
    termsAccepted: { type: 'boolean', default: 0, onCreate: () => false },
    identities: { type: 'string[]', nullable: true },
    born: { type: DateType, nullable: true, length: 3 },
    books: { kind: '1:m', entity: () => 'Book', mappedBy: book => book.author },
    favouriteBook: { kind: 'm:1', type: 'Book' },
    version: { type: 'number', persist: false },
  },
});

Then you can use the entity class as usual:

const author = new Author('name', 'email');
await em.persist(author).flush();

Using custom base entity​

Do not forget that base entities needs to be discovered just like normal entities.

./entities/BaseEntity.ts
export interface CustomBaseEntity {
  id: number;
  createdAt: Date;
  updatedAt: Date;
}

export const schema = new EntitySchema<CustomBaseEntity>({
  name: 'CustomBaseEntity',
  abstract: true,
  properties: {
    id: { type: 'number', primary: true },
    createdAt: { type: 'Date', onCreate: () => new Date(), nullable: true },
    updatedAt: { type: 'Date', onCreate: () => new Date(), onUpdate: () => new Date(), nullable: true },
  },
});

Configuration Reference​

The parameter of EntitySchema requires to provide either name or class parameters. When using class, extends will be automatically inferred. You can optionally pass these additional parameters:

name: string;
class: Constructor<T>;
extends: string;
tableName: string; // alias for `collection: string`
properties: { [K in keyof T & string]: EntityProperty<T[K]> };
indexes: { properties: string | string[]; name?: string; type?: string }[];
uniques: { properties: string | string[]; name?: string }[];
repository: () => Constructor<EntityRepository<T>>;
hooks: Partial<Record<keyof typeof EventType, ((string & keyof T) | NonNullable<EventSubscriber[keyof EventSubscriber]>)[]>>;
abstract: boolean;

Every property then needs to contain a type specification - one of type or entity options. Here are some examples of various property types:

export enum MyEnum {
  LOCAL = 'local',
  GLOBAL = 'global',
}

export const schema = new EntitySchema<FooBar>({
  name: 'FooBar',
  tableName: 'tbl_foo_bar',
  indexes: [{ name: 'idx1', properties: 'name' }],
  uniques: [{ name: 'unq1', properties: ['name', 'email'] }],
  repository: () => FooBarRepository,
  properties: {
    id: { type: 'number', primary: true },
    name: { type: 'string' },
    baz: { kind: '1:1', entity: 'FooBaz', orphanRemoval: true, nullable: true },
    fooBar: { kind: '1:1', entity: 'FooBar', nullable: true },
    publisher: { kind: 'm:1', entity: 'Publisher', inversedBy: 'books' },
    books: { kind: '1:m', entity: () => 'Book', mappedBy: book => book.author },
    tags: { kind: 'm:n', entity: 'BookTag', inversedBy: 'books', fixedOrder: true },
    version: { type: 'Date', version: true, length: 0 },
    type: { enum: true, items: () => MyEnum, default: MyEnum.LOCAL },
  },
});

As a value for type you can also use one of String/Number/Boolean/Date.

defineEntity​

defineEntity is built on top of EntitySchema, leveraging TypeScript's type inference capabilities to generate entity types. This reduces the amount of code while providing robust type safety and null safety.

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

// We use `p` as a shortcut for `defineEntity.properties`
const p = defineEntity.properties;

// It is more recommended to use composition over inheritance when using `defineEntity`
export const baseProperties = {
  id: p.integer().primary(),
  createdAt: p.datetime().onCreate(() => new Date()),
  updatedAt: p.datetime()
    .onCreate(() => new Date())
    .onUpdate(() => new Date()),
};

export const Book = defineEntity({
  name: 'Book',
  properties: p => ({
    ...baseProperties,
    title: p.string(),
    author: () => p.manyToOne(Author).inversedBy('books'),
    publisher: () => p.oneToOne(Publisher).inversedBy('books'),
    tags: () => p.manyToMany(BookTag).inversedBy('books').fixedOrder(),
  }),
});

// We can use `InferEntity` to infer the type of an entity
export interface IBook extends InferEntity<typeof Book> {}

defineEntity.properties provides all MikroORM built-in types. To use custom types, we can also use p.type().

const p = defineEntity.properties;

const properties = {
  string: p.string(),
  float: p.float(),
  boolean: p.boolean(),
  json: p.json<{ foo: string; bar: number }>().nullable(),
  stringArray: p.type(ArrayType<string>).nullable(),
  numericArray: p.type(new ArrayType(i => +i)).nullable(),
  point: p.type(PointType).nullable(),
};

MongoDB example​

export const BookTag = defineEntity({
  name: 'BookTag',
  properties: p => ({
    _id: p.type('ObjectId').primary(),
    id: p.string().serializedPrimaryKey(),
    name: p.string(),
    books: () => p.manyToMany(Book).mappedBy('tags'),
  }),
});

export interface IBookTag extends InferEntity<typeof BookTag> {}

Hooks example​

Entity hooks can be defined either as a property name, or as a function. When defined as a function, the this argument will be the entity instance. Arrow functions can be used if desired, and the entity will be available at args.entity. See Events and Lifecycle Hooks section for more details on EventArgs.

// Defined outside, this available via args.
const beforeUpdate = (args: EventArgs) => args.entity.version++;

export const BookTag = defineEntity({
  name: 'BookTag',
  properties: p => ({
    _id: p.type('ObjectId').primary(),
    id: p.string().serializedPrimaryKey(),
    name: p.string(),
    books: () => p.manyToMany(Book).mappedBy('tags'),
  }),
  hooks: {
    beforeUpdate: [beforeUpdate],
  },
});

export interface IBookTag extends InferEntity<typeof BookTag> {}