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class-fixtures-factory

This lightweight lib is a class factory to generate fixtures on the fly. However, contrarily to most (or rather all) libs out there, class-fixtures-factory generate fixtures from classes. This is handy when you already have classes as your source of truth and do not want to write custom schema to generate fixtures.
Also, because the lib is based on emitted TypeScript's metadata, if you heavily use decorators in your classes (when working with class-validator, type-graphql, for example), the setup will be even easier.

If you aren't familiar about what fixtures are, they are simply randomly generated data and are often used for database seeding or for testing.

Features

  • Generate fixtures on the fly at runtime
  • Leverage faker.js for generating random values
  • Support relationships between classes
  • Customizable
  • Support [email protected] decorators. (type-graphql to come at a latter date)
    Version 0.12.x is broken and doesn't store the decorator names, so it's impossible for this lib to work alongside.

Usage

General

Because class-fixtures-factory relies on metadata, you'll have to:

  1. Register all the classes you're going to use
  2. Annotate properties with decorators Besides the decorators shipped with the lib, you can also use class-validator decorators.
import { FixtureFactory } from 'class-fixtures-factory';

const factory = new FixtureFactory();
factory.register([Author, Address, Book]);

// Generate a fixture
let author = factory.make(Author).one();
// Generate multiple fixtures
let authors = factory.make(Author).many(10);

// Ignore some properties at runtime
const partialAuthor = factory
  .make(Author)
  .ignore('address', 'age')
  .one(); // address and age are undefined

// Override properties at runtime
const agedAuthor = factory
  .make(Author)
  .with({
    age: 70,
    address: specialAddr, // any actual address entity object
  })
  .one();

Customization

As stated previously, you'll need to annotate your class properties somehow, because types metadata are used for generating fixtures. The lib exposes a Fixture decorator for that purpose and for further customization. If your properties are already annotated with decorators from class-validator, there's no need to use Fixture, mostly. However, there are some cases where the Fixture decorator is mandatory;

  • If the type is an array
  • If the type is an enum
class Author {
  // decorator from class-validator
  // no need to use Fixture
  @Length(5, 10)
  name: string;

  @Fixture()
  age: number;

  @Fixture({ type: () => [Book] })
  books: Book[];

  @Fixture({ enum: Mood })
  mood: Mood = Mood.HAPPY;
}

Futhermore, Fixture can be used for further customization, using faker.js, as stated:

export class Author extends BaseEntity {

  @Fixture(faker => faker.name.firstName())
  firstName: string;

  @Fixture('{{name.lastName}}')
  lastName: string;

  @Fixture(() => 24)
  age: number;

  @Fixture({ type: () => [Book] }, { min: 3, max: 5 })
  books: Book[];

  // same as not using @Fixture at all
  @Fixture({ ignore: true })
  address: Address;
}

Factory Options

You can pass an options object to the FixtureFactory constructor:

import { FixtureFactory } from 'class-fixtures-factory';

const factory = new FixtureFactory({ /* options */});

The options parameter can take:

  • debug (boolean) Whether to print generated objects or no.

Assigner

You can provide a function to define how values are assigned to generated objects.

const assigner: Assigner = (prop, obj, value) => {
  // default behavior
  obj[prop.name] = value;
}
factory.setAssigner(assigner);

API

See the API docs page here.