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NestJS Enterprise Backend APIs · 강의

도메인 격리를 위한 포트와 어댑터

구체적인 인프라가 아닌 추상 포트에 의존하게 만들어 비즈니스 로직과 프레임워크를 분리합니다.

레슨 1/413개 단계

도메인 격리를 위한 포트와 어댑터은(는) CoddyKit의 무료 NestJS Enterprise Backend APIs 강의입니다. 이것은 4개 중 1번째 강의입니다. 아래에서 전체 강의를 무료로 읽을 수 있으며, 내장 코드 에디터와 24/7 AI 튜터와 함께 브라우저에서 직접 실습할 수 있습니다. 이 강의는 NestJS Enterprise Backend APIs 학습 경로의 일부이며, 진행 상황이 웹과 CoddyKit 앱에 동기화됩니다. NestJS Enterprise Backend APIs 강의에는 총 4개의 강의가 포함되어 있습니다.

이 강의의 일부는 아직 번역되지 않았으며 영어로 표시됩니다.

Why Isolate the Domain?

In an enterprise NestJS backend, your most valuable code is the business logic: pricing rules, eligibility checks, workflow state machines. This logic should outlive any specific database, message broker, or HTTP framework.

The Ports and Adapters pattern (also called Hexagonal Architecture) achieves this by inverting dependencies. The domain defines abstract ports (interfaces) describing what it needs. Concrete adapters (Postgres, Redis, Stripe) implement those ports and plug in from the outside.

  • The domain depends on nothing external.
  • Infrastructure depends on the domain, never the reverse.

The Dependency Rule

The core invariant is a one-way dependency arrow: infrastructure → application → domain. Source-code imports may only point inward.

A domain entity must never import from @nestjs/common, TypeORM, or an HTTP client. If it does, you have coupled your rules to a framework's release cycle and made them hard to test in isolation.

Ports live inside the boundary; adapters live outside it. The interface (the port) is owned by the domain, so the domain dictates the contract and the outside world conforms to it.

Defining a Driven Port

A driven port (a.k.a. secondary port) is an outbound dependency the domain needs but does not own. Example: persisting an order. The application layer declares an interface describing exactly what it requires, in domain terms.

Notice this file imports nothing from NestJS or a database driver. It is pure TypeScript describing a capability.

export interface Order {
  id: string;
  customerId: string;
  totalCents: number;
  status: 'PENDING' | 'PAID' | 'CANCELLED';
}

// Driven (outbound) port: owned by the application/domain layer.
export interface OrderRepositoryPort {
  save(order: Order): Promise<void>;
  findById(id: string): Promise<Order | null>;
}

A Driving Port: The Use Case

A driving port (primary port) is the entry point into the application, called by the outside world (controllers, CLI, message consumers). It is typically a use-case interface.

The use case orchestrates domain logic and talks to driven ports only through their interfaces. It never knows whether persistence is Postgres or an in-memory map.

export interface PlaceOrderCommand {
  orderId: string;
  customerId: string;
  totalCents: number;
}

// Driving (inbound) port: the application's public contract.
export interface PlaceOrderPort {
  execute(cmd: PlaceOrderCommand): Promise<void>;
}

Implementing the Use Case

The use case implements the driving port and depends on driven ports by their interface type. Here it validates a business rule, builds a domain entity, and delegates persistence to the port.

This class is framework-agnostic. We add NestJS's @Injectable() only as a thin decoration so the DI container can manage it; the logic itself does not depend on Nest at all.

import { Injectable, Inject } from '@nestjs/common';
import { PlaceOrderPort, PlaceOrderCommand } from './place-order.port';
import { OrderRepositoryPort } from './order-repository.port';
import { ORDER_REPOSITORY } from './tokens';

@Injectable()
export class PlaceOrderUseCase implements PlaceOrderPort {
  constructor(
    @Inject(ORDER_REPOSITORY)
    private readonly orders: OrderRepositoryPort,
  ) {}

  async execute(cmd: PlaceOrderCommand): Promise<void> {
    if (cmd.totalCents <= 0) {
      throw new Error('Order total must be positive');
    }
    await this.orders.save({
      id: cmd.orderId,
      customerId: cmd.customerId,
      totalCents: cmd.totalCents,
      status: 'PENDING',
    });
  }
}

Injection Tokens for Interfaces

TypeScript interfaces vanish at runtime, so NestJS cannot use them as DI keys directly. The idiom is to define a string or symbol token and bind the port to a concrete adapter in the module.

Always reference the token with @Inject(TOKEN) at injection sites. Symbols avoid accidental string collisions across modules.

export const ORDER_REPOSITORY = Symbol('OrderRepositoryPort');
export const PLACE_ORDER = Symbol('PlaceOrderPort');

// Usage at an injection site:
// constructor(@Inject(ORDER_REPOSITORY) repo: OrderRepositoryPort) {}

Writing a Driven Adapter

An adapter implements a driven port using concrete infrastructure. Here a TypeORM adapter satisfies OrderRepositoryPort. It maps between the persistence model and the domain Order, keeping the database schema out of the domain.

The domain never sees OrderEntity or the repository — only the port. Swap to MongoDB tomorrow by writing a new adapter; the use case stays untouched.

import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { OrderRepositoryPort, Order } from '../application/order-repository.port';
import { OrderEntity } from './order.entity';

@Injectable()
export class TypeOrmOrderRepository implements OrderRepositoryPort {
  constructor(
    @InjectRepository(OrderEntity)
    private readonly repo: Repository<OrderEntity>,
  ) {}

  async save(order: Order): Promise<void> {
    await this.repo.save(this.repo.create(order));
  }

  async findById(id: string): Promise<Order | null> {
    const row = await this.repo.findOne({ where: { id } });
    return row ? { ...row } : null;
  }
}

Wiring Ports to Adapters in a Module

The NestJS module is the composition root where ports meet adapters. Use provide with the token and useClass with the concrete adapter. This is the only place that knows both sides.

Because binding happens here, the entire domain remains ignorant of TypeORM. Tests can supply a different binding without modifying any business code.

import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';
import { OrderEntity } from './infrastructure/order.entity';
import { TypeOrmOrderRepository } from './infrastructure/typeorm-order.repository';
import { PlaceOrderUseCase } from './application/place-order.usecase';
import { ORDER_REPOSITORY, PLACE_ORDER } from './application/tokens';

@Module({
  imports: [TypeOrmModule.forFeature([OrderEntity])],
  providers: [
    { provide: ORDER_REPOSITORY, useClass: TypeOrmOrderRepository },
    { provide: PLACE_ORDER, useClass: PlaceOrderUseCase },
  ],
  exports: [PLACE_ORDER],
})
export class OrdersModule {}

The Controller is Just Another Adapter

An HTTP controller is a driving adapter: it translates a transport-specific request into a call on the driving port. It holds no business logic — just mapping and delegation.

Replacing REST with gRPC or a Kafka consumer means writing a new driving adapter against the same PlaceOrderPort. The use case never changes.

import { Body, Controller, Inject, Post } from '@nestjs/common';
import { PlaceOrderPort } from '../application/place-order.port';
import { PLACE_ORDER } from '../application/tokens';

@Controller('orders')
export class OrdersController {
  constructor(
    @Inject(PLACE_ORDER) private readonly placeOrder: PlaceOrderPort,
  ) {}

  @Post()
  async create(@Body() body: { orderId: string; customerId: string; totalCents: number }) {
    await this.placeOrder.execute(body);
    return { status: 'accepted' };
  }
}

Testing With an In-Memory Adapter

The biggest payoff is testability. Because the use case depends on a port, you test it with a trivial in-memory adapter — no database, no Nest container, no mocking framework.

This snippet is a complete standalone program: it defines the port, a fake adapter, the use case, and runs an assertion. It demonstrates that the domain logic is fully exercisable in isolation.

interface Order {
  id: string;
  customerId: string;
  totalCents: number;
  status: 'PENDING' | 'PAID' | 'CANCELLED';
}

interface OrderRepositoryPort {
  save(order: Order): Promise<void>;
  findById(id: string): Promise<Order | null>;
}

class InMemoryOrderRepo implements OrderRepositoryPort {
  private store = new Map<string, Order>();
  async save(o: Order) { this.store.set(o.id, o); }
  async findById(id: string) { return this.store.get(id) ?? null; }
}

class PlaceOrderUseCase {
  constructor(private readonly orders: OrderRepositoryPort) {}
  async execute(cmd: { orderId: string; customerId: string; totalCents: number }) {
    if (cmd.totalCents <= 0) throw new Error('Order total must be positive');
    await this.orders.save({ ...cmd, id: cmd.orderId, status: 'PENDING' });
  }
}

async function main() {
  const repo = new InMemoryOrderRepo();
  const useCase = new PlaceOrderUseCase(repo);
  await useCase.execute({ orderId: 'o1', customerId: 'c1', totalCents: 4200 });
  const saved = await repo.findById('o1');
  console.log(saved?.status === 'PENDING' ? 'PASS' : 'FAIL');
}

main();

Anti-Corruption at the Boundary

Adapters double as an anti-corruption layer. External shapes — a Stripe webhook payload, a third-party DTO — must be translated into clean domain types inside the adapter, never leaked inward.

  • Keep mapping logic in the adapter, not the use case.
  • Never let a vendor's enum or snake_case field reach a domain entity.
  • Validate and normalize at the edge so the core trusts its inputs.

This discipline is what keeps the hexagon's interior stable while the messy outside world churns.

import { PaymentPort } from '../application/payment.port';

// Adapter translates a vendor payload into a domain-friendly result.
export class StripePaymentAdapter implements PaymentPort {
  async charge(customerId: string, amountCents: number): Promise<{ paid: boolean }> {
    const vendorResp = await this.callStripe(customerId, amountCents);
    // Map vendor shape -> domain shape (anti-corruption).
    return { paid: vendorResp.status === 'succeeded' };
  }

  private async callStripe(_c: string, _a: number) {
    return { status: 'succeeded' as const };
  }
}

Quick Check

Consider a NestJS use case that must persist data. Where should the persistence interface (the port) be defined, and who implements it?

인터랙티브 레슨에서 답해보세요

Recap

You isolated the domain from frameworks using Ports and Adapters:

  • Ports are interfaces owned by the domain/application layer — driving (inbound use cases) and driven (outbound dependencies like repositories).
  • Adapters live outside the boundary and implement driven ports or call driving ports.
  • The dependency rule forces all imports to point inward; the domain depends on nothing external.
  • In NestJS, bind ports to adapters in the module using injection tokens (symbols), since interfaces disappear at runtime.
  • The payoff: swap infrastructure freely and test business logic in isolation with simple in-memory adapters.
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자주 묻는 질문

“도메인 격리를 위한 포트와 어댑터” 강의는 무료인가요?

네 — “도메인 격리를 위한 포트와 어댑터” 전체 내용을 이 웹사이트에서 무료로 읽을 수 있습니다. 인터랙티브하게 실습하려면(내장 코드 에디터와 24/7 AI 튜터), CoddyKit PRO로 업그레이드하면 NestJS Enterprise Backend APIs 강의 전체를 잠금 해제할 수 있습니다. NestJS Enterprise Backend APIs 강의에는 총 4개의 강의가 포함되어 있습니다.

“도메인 격리를 위한 포트와 어댑터”에서 뭘 배우나요?

구체적인 인프라가 아닌 추상 포트에 의존하게 만들어 비즈니스 로직과 프레임워크를 분리합니다. 브라우저에서 직접 실행하는 실습 코드로 NestJS Enterprise Backend APIs을(를) 배우며, 24/7 AI 튜터가 강의를 진행하면서 질문에 답변해줍니다.

NestJS Enterprise Backend APIs을(를) 시작하는 데 경험이 필요한가요?

사전 경험은 필요하지 않습니다. CoddyKit의 NestJS Enterprise Backend APIs은(는) 초급자부터 고급 학습자까지를 위해 구성되어 있으므로, 여기서 시작하거나 처음부터 시작할 수 있으며 자신의 속도대로 진행할 수 있습니다. 이것은 4개 중 1번째 강의입니다.

“도메인 격리를 위한 포트와 어댑터” 강의는 얼마나 걸리나요?

대부분의 CoddyKit 강의는 약 5~10분이 소요됩니다. 각 강의는 간결하고 인터랙티브하여 꾸준한 진행이 가능하며, 웹과 앱에서 중단한 부분부터 바로 시작할 수 있습니다.

이 NestJS Enterprise Backend APIs 강의에서 코드를 작성하고 실행할 수 있나요?

네. 모든 NestJS Enterprise Backend APIs 강의에는 내장 코드 에디터가 포함되어 있으므로, 브라우저에서 바로 실제 코드를 작성하고 실행한 후 즉시 AI 피드백을 받을 수 있습니다 — 로컬 설정이 필요 없습니다.

이 강의의 모든 강의

  1. 도메인 격리를 위한 포트와 어댑터
  2. DiscoveryService를 활용한 동적 공급자 등록
  3. 지연 로딩 모듈과 기능 토글
  4. 모듈 참조 API를 활용한 확장 지점
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