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
• Usage
  • General
  • Using class-validator metadatas
  • Using class-validator custom validators
  • Customization
  • Property dependencies
  • Factory Options
    • Assigner
  • API

Features

• Generate fixtures on the fly at runtime
• Leverage faker.js for generating random values
• Support relationships between classes
• Support property dependencies
• Customizable
• Support [email protected] decorators. (type-graphql to come at a latter date)

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();
// these classes are annotated. See further below
factory.register([Author, Address, Book]);

// Generate a fixture
const author = factory.make(Author).one();
// Generate multiple fixtures
const 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();

Using class-validator metadatas

If you happen to use class-validator decorators for your entities, you can generate fixtures from them, as long as you import class-fixtures-factory/plugins/class-validator somewhere in your entry point.

import 'class-fixtures-factory/plugins/class-validator';

Note that this will require having class-validator version 0.14 or higher to be installed.

Using class-validator custom validators

If you declare custom class-validator validators, you can hook into metadata extraction to override data generation for the property.

function IsFullName(validationOptions?: ValidationOptions) {
  return (object: Object, propertyName: string) => {
    registerDecorator({
      target: object.constructor,
      name: 'isFullName',
      propertyName,
      options: validationOptions,
      constraints: [],
      validator: {
        validate(value: any, validationArguments: ValidationArguments) {
          return contains(value, ' ');
        },
        defaultMessage(validationArguments: ValidationArguments) {
          return 'Invalid full name';
        }
      },
    });
  };
}

class DummyPerson {
  @IsFullName()
  name!: string;
}

factory.setOptions({
  customValidators(faker, prop, _reflectProp, cvMeta, propHooks) {
    switch (cvMeta.name) {
      case 'isFullName':
        propHooks.setOverride(() => faker.person.fullName());
        prop.type = 'string';
        break;
    }
  },
})

factory.make(DummyPerson).one();

You can view the source code to learn how to override metadata declaration.

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 property type is an array
• If the property type is an enum

class Author {
  // decorator from class-validator
  // no need to use Fixture if you use the plugin
  @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.
Note however that using Fixture will override other decorators from class-validator.

export class Author extends BaseEntity {

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

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

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

  @Enum()
  mood: Mood;

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

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

  // when generated, will always be 500
  @IsNumber()
  @Fixture(() => 500)
  superAge: number;

  // is ignored
  @IsString()
  @Fixture({ ignore: true })
  hiddenName: string;
}

Property dependencies

You can also declare dependencies that your class property lies upon to have its value generated.

With the dependsOn option in Fixture, a property can mark other instance property as its dependency. All dependencies are resolved before the property itself, and the resolved values can be used in Fixture generator.

export class Person extends BaseEntity {
  @Fixture(faker => faker.person.fullName())
  name!: string;

  @Fixture(faker => faker.number.int({ min: 0, max: 100 }))
  age!: number;

  @Fixture({ get: (faker, age) => age >= 18, dependsOn: ['age'] })
  isAdult!: boolean;

  @Fixture({ get: (faker, name, age) => `I'm ${name}, and I'm ${age} years old.`, dependsOn: ['name', 'age'] })
  bio!: string;
}

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.

• fakerInstance (Faker) Faker instance to be used. Useful for localized data generation

  import { fakerPT_BR } from '@faker-js/faker';
    
  const result = factory.make(DummyClass, {
    fakerInstance: fakerPT_BR,
  }).one();

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.