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?: Date;
  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.

MongoDB example

export class BookTag {
  _id!: ObjectId;
  id!: string;
  name: string;
  books = new Collection<Book>(this);

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

export const schema = new EntitySchema<BookTag>({
  class: BookTag,
  properties: {
    _id: { type: 'ObjectId', primary: true },
    id: { type: 'string', serializedPrimaryKey: true },
    name: { type: 'string' },
    books: { kind: 'm:n', entity: () => Book, mappedBy: book => book.tags },
  },
});

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.

export class BookTag {
  _id!: ObjectId;
  id!: string;
  name: string;
  books = new Collection<Book>(this);

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

  // Defined on an entity class.
  beforeCreate() {
    this.version = 1;
  }

  beforeUpdate() {
    this.version++;
  }
}

// Defined outside of entity class - this bound to entity instance
function beforeUpdate() {
  this.version++;
}

// Defined outside, this available via args.
const beforeUpdate2 = (args: EventArgs) => args.entity.version++;

export const schema = new EntitySchema({
  class: BookTag,
  hooks: {
    beforeCreate: ['beforeCreate'], // Instance method
    beforeUpdate: ['beforeUpdate', beforeUpdate, beforeUpdate2] // Instance method, normal function, arrow function
  },
  properties: {
    _id: { type: 'ObjectId', primary: true },
    id: { type: 'string', serializedPrimaryKey: true },
    name: { type: 'string' },
    books: { kind: 'm:n', entity: () => Book, mappedBy: book => book.tags },
  },
});