NestJS Enterprise Backend APIs · 课时

使用参数装饰器读取请求上下文

使用 createParamDecorator 和 ExecutionContext 创建自定义的 @CurrentUser 与 @ClientIp 参数装饰器。

第 1 / 4 课13 个步骤

使用参数装饰器读取请求上下文 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 Param Decorators?

In NestJS controllers, you often need to pull the same piece of data out of the request over and over: the authenticated user, the client IP, a tenant id from a header. Doing this with @Req() and digging into request.user in every handler is repetitive and leaks framework details into your business logic.

Custom param decorators let you encapsulate that extraction once and reuse it everywhere:

@CurrentUser() instead of req.user
@ClientIp() instead of parsing x-forwarded-for

The result is cleaner, more testable, and more declarative controller code.

The Repetitive Way

Here is what you usually start with: grabbing the whole request object and reaching into it manually. It works, but every handler repeats the same lines, and the controller now knows about request.user, which is an implementation detail of your auth guard.

Notice how the actual route logic is buried under plumbing. This is exactly what a param decorator removes.

import { Controller, Get, Req } from '@nestjs/common';
import { Request } from 'express';

@Controller('profile')
export class ProfileController {
  @Get()
  getProfile(@Req() request: Request) {
    const user = (request as any).user;
    return { id: user.id, email: user.email };
  }
}

createParamDecorator

NestJS exposes the factory createParamDecorator from @nestjs/common. You give it a function that receives two arguments and returns whatever value you want injected into the handler parameter.

data — the optional argument passed when the decorator is used, e.g. @CurrentUser('email').
ctx: ExecutionContext — a wrapper around the current request context, independent of the transport (HTTP, RPC, WebSocket).

The returned value becomes the parameter's value at call time.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';

export const Example = createParamDecorator(
  (data: unknown, ctx: ExecutionContext) => {
    // return any value -> it gets injected into the param
    return 'hello';
  },
);

Getting the HTTP Request

For HTTP apps you convert the generic ExecutionContext into an HTTP-specific argument host and read the request from it:

ctx.switchToHttp() returns an HttpArgumentsHost.
.getRequest() gives you the underlying request (Express or Fastify).

Using switchToHttp() keeps the decorator explicit about which transport it targets. The same context could also be switched to RPC or WS for other protocols.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';
import { Request } from 'express';

export const RawRequest = createParamDecorator(
  (data: unknown, ctx: ExecutionContext): Request => {
    return ctx.switchToHttp().getRequest<Request>();
  },
);

Building @CurrentUser

Assume an auth guard (e.g. a JWT strategy) has already attached the authenticated user to request.user. The @CurrentUser() decorator simply returns it.

This is the canonical pattern in enterprise NestJS apps: the guard does authentication, and the decorator gives ergonomic access to the result without exposing the request object.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';

export interface AuthUser {
  id: string;
  email: string;
  roles: string[];
}

export const CurrentUser = createParamDecorator(
  (data: unknown, ctx: ExecutionContext): AuthUser => {
    const request = ctx.switchToHttp().getRequest();
    return request.user;
  },
);

Using the data Argument

The first parameter, data, is what the caller passes inside the decorator's parentheses. You can use it to return a single property instead of the whole object:

@CurrentUser() returns the full user.
@CurrentUser('email') returns just the email.

Type the data argument as keyof AuthUser so the caller gets autocomplete and compile-time safety on the property name.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';
import { AuthUser } from './auth-user.interface';

export const CurrentUser = createParamDecorator(
  (data: keyof AuthUser | undefined, ctx: ExecutionContext) => {
    const request = ctx.switchToHttp().getRequest();
    const user: AuthUser = request.user;
    return data ? user?.[data] : user;
  },
);

Consuming @CurrentUser in a Controller

Now the controller reads beautifully. The guard guarantees the user exists; the decorator injects exactly what each handler needs. No @Req(), no manual property digging.

This separation is what makes the handler easy to unit-test: you just call the method with a plain user object.

import { Controller, Get, UseGuards } from '@nestjs/common';
import { JwtAuthGuard } from './jwt-auth.guard';
import { CurrentUser } from './current-user.decorator';
import { AuthUser } from './auth-user.interface';

@UseGuards(JwtAuthGuard)
@Controller('me')
export class MeController {
  @Get()
  getMe(@CurrentUser() user: AuthUser) {
    return user;
  }

  @Get('email')
  getEmail(@CurrentUser('email') email: string) {
    return { email };
  }
}

Building @ClientIp

Behind a load balancer or reverse proxy, the real client IP is not request.ip but the first entry of the x-forwarded-for header. A @ClientIp() decorator centralizes this logic so every handler reads the correct address.

Important: only trust x-forwarded-for when you actually run behind a trusted proxy, and enable Express's trust proxy setting. Otherwise clients can spoof the header.

import { createParamDecorator, ExecutionContext } from '@nestjs/common';
import { Request } from 'express';

export const ClientIp = createParamDecorator(
  (data: unknown, ctx: ExecutionContext): string => {
    const request = ctx.switchToHttp().getRequest<Request>();
    const forwarded = request.headers['x-forwarded-for'];
    if (typeof forwarded === 'string' && forwarded.length > 0) {
      return forwarded.split(',')[0].trim();
    }
    return request.ip ?? '';
  },
);

Pure Extraction Logic Is Testable

The valuable part of a param decorator is its pure extraction logic. You can lift that into a plain function, unit-test it with a fake request, and call it from the decorator. Here is the IP-parsing logic as a standalone, runnable program.

This demonstrates the rule for choosing the first forwarded address and the fallback behavior — no NestJS or server required to verify it.

function extractClientIp(headers: Record<string, string>, fallbackIp: string): string {
  const forwarded = headers['x-forwarded-for'];
  if (typeof forwarded === 'string' && forwarded.length > 0) {
    return forwarded.split(',')[0].trim();
  }
  return fallbackIp;
}

console.log(extractClientIp({ 'x-forwarded-for': '203.0.113.7, 70.41.3.18' }, '10.0.0.1'));
console.log(extractClientIp({}, '10.0.0.1'));
console.log(extractClientIp({ 'x-forwarded-for': '198.51.100.5' }, '10.0.0.1'));

Combining Decorators in One Handler

Param decorators compose freely. A single handler can mix built-in decorators (@Body, @Param) with your custom ones. NestJS resolves each parameter independently by its decorator metadata.

Here an audit endpoint records who did what and from where, reading the user and IP declaratively.

import { Controller, Post, Body, UseGuards } from '@nestjs/common';
import { JwtAuthGuard } from './jwt-auth.guard';
import { CurrentUser } from './current-user.decorator';
import { ClientIp } from './client-ip.decorator';
import { AuthUser } from './auth-user.interface';

@UseGuards(JwtAuthGuard)
@Controller('audit')
export class AuditController {
  @Post('action')
  record(
    @CurrentUser('id') userId: string,
    @ClientIp() ip: string,
    @Body() body: { action: string },
  ) {
    return { userId, ip, action: body.action, at: new Date().toISOString() };
  }
}

Validation and Pipes Still Apply

A custom param decorator returns a raw value, so you can still attach pipes to it just like built-in decorators. Pass a pipe as an extra argument when using the decorator.

@CurrentUser('id', ParseUUIDPipe) validates that the extracted id is a UUID.
Pipes run after the decorator factory returns its value.

This lets you keep extraction and validation cleanly separated while still benefiting from NestJS's pipe pipeline.

import { Controller, Get, ParseUUIDPipe } from '@nestjs/common';
import { CurrentUser } from './current-user.decorator';

@Controller('orders')
export class OrdersController {
  @Get('mine')
  myOrders(@CurrentUser('id', ParseUUIDPipe) userId: string) {
    return { userId };
  }
}

Quick Check

Test your understanding of how a custom param decorator reads the request.

在交互式课程中回答

Recap

You learned to read request context declaratively with custom param decorators:

createParamDecorator((data, ctx) => ...) builds a reusable decorator; the returned value is injected into the handler parameter.
ctx.switchToHttp().getRequest() retrieves the HTTP request in a transport-explicit way.
@CurrentUser() wraps request.user (populated by your auth guard) and can return a single property via the data argument typed as keyof AuthUser.
@ClientIp() centralizes x-forwarded-for parsing, with a fallback to request.ip — trust the header only behind a real proxy.
Keep extraction logic pure so it is easy to unit-test, and remember you can still chain pipes like ParseUUIDPipe onto your custom decorators.

免费开始

用 AI 导师学习 TypeScript — 免费

在浏览器中编写并运行真实代码，获得全天候 AI 导师的即时帮助，并在网页或应用中继续学习。

课程: 20
课程: 76

免费开始学习查看完整课程

常见问题解答

「使用参数装饰器读取请求上下文」课时是免费的吗？

是的 — 「使用参数装饰器读取请求上下文」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。

「使用参数装饰器读取请求上下文」这节课中我会学到什么？

使用 createParamDecorator 和 ExecutionContext 创建自定义的 @CurrentUser 与 @ClientIp 参数装饰器。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。

「使用参数装饰器读取请求上下文」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。

此课程中的所有课时

← 返回 NestJS Enterprise Backend APIs