用于领域隔离的端口与适配器
依赖抽象端口而非具体基础设施，使业务逻辑与框架解耦。
用于领域隔离的端口与适配器 是 CoddyKit 上的免费 NestJS Enterprise Backend APIs 课时。 这是第 1 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 NestJS Enterprise Backend APIs 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 NestJS Enterprise Backend APIs 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
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?
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.
常见问题解答
「用于领域隔离的端口与适配器」课时是免费的吗？
是的 — 「用于领域隔离的端口与适配器」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 NestJS Enterprise Backend APIs 课程的其余内容，请升级到 CoddyKit PRO。 NestJS Enterprise Backend APIs 课程共包含 4 节课。
「用于领域隔离的端口与适配器」这节课中我会学到什么？
依赖抽象端口而非具体基础设施，使业务逻辑与框架解耦。 你通过在浏览器中直接运行的动手代码来练习 NestJS Enterprise Backend APIs，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 NestJS Enterprise Backend APIs 需要有经验吗？
无需任何先前经验。CoddyKit 上的 NestJS Enterprise Backend APIs 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 1 节课，共 4 节。
「用于领域隔离的端口与适配器」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 NestJS Enterprise Backend APIs 课中编写并运行代码吗？
能。每节 NestJS Enterprise Backend APIs 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。