Defining Entities

Entities are simple javascript objects (so called POJO), decorated with @Entity decorator. No real restrictions are made, you do not have to extend any base class, you are more than welcome to use entity constructors, just do not forget to specify primary key with @PrimaryKey decorator.

./entities/Book.ts

@Entity()
export class Book implements IdEntity<Book> {
@PrimaryKey()
id!: number;
@Property()
createdAt = new Date();
@Property({ onUpdate: () => new Date() })
updatedAt = new Date();
@Property()
title!: string;
@ManyToOne() // when you provide correct type hint, ORM will read it for you
author!: Author;
@ManyToOne(() => Publisher) // or you can specify the entity as class reference or string name
publisher?: Publisher;
@ManyToMany() // owning side can be simple as this!
tags = new Collection<BookTag>(this);
constructor(title: string, author: Author) {
this.title = title;
this.author = author;
}
}

You will need to mark the entity by implementing one of *Entity interfaces:

  • IdEntity<T> for numeric/string PK on id property (id: number)
  • UuidEntity<T> for string PK on uuid property (uuid: string)
  • MongoEntity<T> for mongo, where id: string and _id: ObjectId are required
  • AnyEntity<T, PK> for other possible properties (fill the PK property name to PK parameter, e.g.: AnyEntity<Book, 'myPrimaryProperty'>')

As you can see, entity properties are decorated either with @Property decorator, or with one of reference decorators: @ManyToOne, @OneToMany, @OneToOne and @ManyToMany.

Here is another example of Author entity, that was referenced from the Book one, this time defined for mongo:

./entities/Author.ts

@Entity()
export class Author implements MongoEntity<Author> {
@PrimaryKey()
_id!: ObjectId;
@SerializedPrimaryKey()
id!: string;
@Property()
createdAt = new Date();
@Property({ onUpdate: () => new Date() })
updatedAt = new Date();
@Property()
name!: string;
@Property()
email!: string;
@Property()
age?: number;
@Property()
termsAccepted = false;
@Property()
identities?: string[];
@Property()
born?: Date;
@OneToMany(() => Book, book => book.author)
books = new Collection<Book>(this);
@ManyToMany()
friends = new Collection<Author>(this);
@ManyToOne()
favouriteBook?: Book;
@Property({ version: true })
version!: number;
constructor(name: string, email: string) {
this.name = name;
this.email = email;
}
}

More information about modelling relationships can be found on modelling relationships page.

If you want to define your entity in Vanilla JavaScript, take a look here.

Optional Properties

When you define the property as optional (marked with ?), this will be automatically considered as nullable property (mainly for SQL schema generator).

This auto-detection works only when you omit the type attribute.

Enums

To define enum property, use @Enum() decorator. Enums can be either numeric or string valued.

For schema generator to work properly in case of string enums, you need to define the enum is same file as where it is used, so its values can be automatically discovered. If you want to define the enum in another file, you should reexport it also in place where you use it.

You can also set enum items manually via items: string[] attribute.

@Entity()
export class User implements IdEntity<User> {
@Enum()
role!: UserRole; // string enum
@Enum()
status!: UserStatus; // numeric enum
}
export enum UserRole {
ADMIN = 'admin',
MODERATOR = 'moderator',
USER = 'user',
}
export const enum UserStatus {
DISABLED,
ACTIVE,
}

Virtual Properties

You can define your properties as virtual, either as a method, or via JavaScript get/set.

Following example defines User entity with firstName and lastName database fields, that are both hidden from the serialized response, replaced with virtual properties fullName (defined as a classic method) and fullName2 (defined as a JavaScript getter).

For JavaScript getter you need to provide { persist: false } option otherwise the value would be stored in the database.

@Entity()
export class User implements IdEntity<User> {
@Property({ hidden: true })
firstName!: string;
@Property({ hidden: true })
lastName!: string;
@Property({ name: 'fullName' })
getFullName() {
return `${this.firstName} ${this.lastName}`;
}
@Property({ persist: false })
get fullName2() {
return `${this.firstName} ${this.lastName}`;
}
}
const repo = orm.em.getRepository(User);
const author = repo.create({ firstName: 'Jon', lastName: 'Snow' });
console.log(author.getFullName()); // 'Jon Snow'
console.log(author.fullName2); // 'Jon Snow'
console.log(author.toJSON()); // { fullName: 'Jon Snow', fullName2: 'Jon Snow' }

Entity file names

You are free to choose one of those formats for entity filename (for a BookTag entity):

  • BookTag.ts
  • BookTag.model.ts
  • book-tag.ts
  • book-tag.model.ts
  • book-tag.entity.ts

Entity name is inferred from the first part of file name before first dot occurs, so you can add any suffix behind the dot, not just .model.ts or .entity.ts.

You can change this behaviour by defining custom NamingStrategy.getClassName() method.

Using BaseEntity

You can define your own base entity with properties that you require on all entities, like primary key and created/updated time.

If you are initializing the ORM via entities option, you need to specify all your base entities as well.

./entities/BaseEntity.ts

import { v4 } from 'uuid';
export abstract class BaseEntity implements UuidEntity<BaseEntity> {
@PrimaryKey()
uuid = v4();
@Property()
createdAt = new Date();
@Property({ onUpdate: () => new Date() })
updatedAt = new Date();
}

Examples of entity definition with various primary keys

Using id as primary key (SQL drivers)

@Entity()
export class Book implements IdEntity<Book> {
@PrimaryKey()
id!: number; // string is also supported
@Property()
title!: string;
@ManyToOne()
author!: Author;
}

Using UUID as primary key (SQL drivers)

import { v4 } from 'uuid';
@Entity()
export class Book implements UuidEntity<Book> {
@PrimaryKey()
uuid = v4();
@Property()
title!: string;
@ManyToOne()
author!: Author;
}

Example of Mongo entity

@Entity()
export class Book implements MongoEntity<Book> {
@PrimaryKey()
_id!: ObjectId;
@SerializedPrimaryKey()
id!: string; // string variant of PK, will be handled automatically
@Property()
title!: string;
@ManyToOne()
author!: Author;
}

Using WrappedEntity interface

@Entity()
export class Book {
@PrimaryKey()
id!: number;
@Property()
title!: string;
@ManyToOne()
author!: Author;
}
export interface Book extends WrappedEntity<Book, 'id'> { };

With your entities set up, you can start using entity manager and repositories as described in following sections.