DTO & Builder Pattern

This is a simple library for defining DTO (data transfer object) classes with decorators, and automatically generating builder classes to simplify defining a DTO's data.

NPM

Installing

npm i -s @jest-automation/dto

DTOs

A DTO is a class with the @Property decorator applied to at least one property.

For example:

import { Property } from '@jest-automation/dto';

export class CreateUserDto {
  @Property
  username!: string;

  @Property
  password!: string;

  @Property
  email?: string;
}

Builders

Now it's possible to generate a builder for this DTO. By passing a DTO Class to the Builder function, a new class will be created with builder functions corresponding to the DTO properties.

import { CreateUserDto } from './somewhere';
import { Builder } from '@jest-automation/dto';

const CreateUserBuilder = Builder(CreateUserDTO);

const builder = new CreateUserBuilder();

The builder will share property names with the underlying DTO, which will be methods that take a value to fill in the DTO, and which return the builder instance to allow for chaining.

builder.username('fredici').password('1234');

Type information is generated preventing the wrong type being used for a param unless explicitly bypassed

builder.username(1); // tsc error
builder.username(1 as unknown as string); // ok

To retrieve the underlying DTO, call the build method.

const result = builder.build();

If the package class-validators is being used, then their validation will be executed by the build method. To disable validation, pass false to the build method.

const result = builder.build(false);