The NestJS Expandable Library is a powerful and flexible extension for NestJS applications, providing a generic pattern for resource expansion in REST APIs. It allows you to dynamically expand and include related resources in API responses, enhancing the flexibility of your API design.

• Dynamic Resource Expansion: Easily expand related resources in API responses using query parameters.
• Dynamic Field Selection: Easily select only the fields you want to get from the API responses using query parameters.
• Decorator-Based Configuration: Use decorators to mark classes and methods as expanders and expandable, simplifying configuration.
• Enhanced Metadata Handling: Improved handling of metadata allows for multiple decorators of the same type on the same target.
• Configuration and Customization: Configure and customize the library to suit your application's specific needs.
• Error Handling: Graceful handling of errors during expansion with customizable logging options.
• Tested and Reliable: Extensive unit tests ensure the reliability of the library.

yarn add @golevelup/nestjs-discovery @cisstech/nestjs-expand

• 1. Decorate Expandable Endpoints

  // user.controller.ts
  import { Controller, Get, NotFoundException } from '@nestjs/common'
  import { Expandable } from '@cisstech/nestjs-expand'
  import { UserDTO } from './user.dto'
  import { UserService } from './user.service'
  
  @Controller('users')
  export class UserController {
    constructor(private readonly userService: UserService) {}
  
    @Get(':id')
    @Expandable(UserDTO)
    async getById(@Param('id') id: string): Promise<UserDTO> {
      const user = await this.userService.getById(id)
      if (!user) {
        throw new NotFoundException(`User not found: ${id}`)
      }
      return new UserDTO(user)
    }
  }

• 2. Implement Expander Services

  // user.expander.ts
  import { Injectable, NotFoundException } from '@nestjs/common'
  import { ExpandContext, Expander, Expandable } from '@cisstech/nestjs-expand'
  import { UserDTO } from './user.dto'
  import { CustomerService } from './user.service'
  
  @Injectable()
  @Expander(UserDTO)
  export class UserExpander {
    constructor(private readonly customerService: CustomerService) {}
  
    async customer(context: ExpandContext<Request, UserDTO>): Promise<CustomerDTO> {
      const user = context.parent
      const customer = await this.customerService.getById(user.customerId)
      if (!customer) {
        throw new NotFoundException(`Customer not found: ${user.customerId}`)
      }
      return new CustomerDTO(customer)
    }
  }

• 3. Register the controllers and expanders

// app.module.ts

import { Module } from '@nestjs/common'
import { NestKitExpandModule } from '@cisstech/nestjs-expand'
import { UserExpander } from 'PATH_TO_FILE'
import { UserController } from 'PATH_TO_FILE'

@Module({
  imports: [NestKitExpandModule.forRoot()],
  controllers: [UserController],
  providers: [UserExpander],
})
export class AppModule {}

The library provides configuration options to customize its behavior. You can pass an optional configuration object when initializing the ExpandService in your module.

// app.module.ts

import { Module } from '@nestjs/common'
import { NestKitExpandModule } from '@cisstech/nestjs-expand'
import { UserExpander } from 'PATH_TO_FILE'
import { UserController } from 'PATH_TO_FILE'

@Module({
  imports: [
    NestKitExpandModule.forRoot({
      enableLogging: true,
      enableGlobalSelection: true,
    }),
  ],
  controllers: [UserController],
  providers: [UserExpander],
})
export class AppModule {}

For detailed documentation, examples, and advanced usage, please refer to the official documentation at https://cisstech.github.io/nestkit/docs/nestjs-expand/getting-started

A presentation article is also available medium

MIT © Mamadou Cisse