如何在Mongoose的pre和post钩子中获取请求唯一标识？

核心问题原因 #

你遇到的$locals未定义问题，是因为最新版Mongoose的Query实例（查询钩子中的this）并没有内置$locals属性，该属性通常用于文档钩子（如save、remove）的上下文，而非查询操作的上下文。

可行解决方案 #

方案一：直接给Query实例添加自定义属性（TypeScript友好）

Mongoose允许直接给Query实例添加自定义属性，只需通过TypeScript扩展类型消除类型报错即可：

1. 扩展Mongoose Query类型（创建类型声明文件，比如src/types/mongoose.d.ts）：

import 'mongoose';

declare module 'mongoose' {
  interface Query<ResultType, DocType, THelpers = {}, RawDocType = DocType> {
    requestId?: number;
    startTime?: number;
  }
}

2. 修改钩子代码：

let count = 0;

UserSchema.pre(/.*/, async function() {
  this.requestId = count++;
  this.startTime = Date.now();
  console.log(`Pre - Request id: ${this.requestId}`);
});

UserSchema.post(/.*/, function() {
  const duration = Date.now() - this.startTime!;
  console.log(`Post - Request id: ${this.requestId}, 耗时: ${duration}ms`);
});

方案二：使用Symbol避免属性命名冲突

如果担心自定义属性和Mongoose内置属性冲突，用Symbol作为属性键：

import 'mongoose';

const REQUEST_ID = Symbol('requestId');
const START_TIME = Symbol('startTime');

// 扩展类型
declare module 'mongoose' {
  interface Query<ResultType, DocType, THelpers = {}, RawDocType = DocType> {
    [REQUEST_ID]?: number;
    [START_TIME]?: number;
  }
}

let count = 0;

UserSchema.pre(/.*/, async function() {
  this[REQUEST_ID] = count++;
  this[START_TIME] = Date.now();
  console.log(`Pre - Request id: ${this[REQUEST_ID]}`);
});

UserSchema.post(/.*/, function() {
  const duration = Date.now() - this[START_TIME]!;
  console.log(`Post - Request id: ${this[REQUEST_ID]}, 耗时: ${duration}ms`);
});

方案三：结合NestJS请求上下文关联HTTP请求

如果需要将数据库查询与HTTP请求关联，用NestJS的AsyncLocalStorage传递请求ID：

1. 创建异步存储工具：

// src/utils/async-local-storage.ts
import { AsyncLocalStorage } from 'async_hooks';

export const asyncLocalStorage = new AsyncLocalStorage<{ requestId: string }>();

2. 实现请求ID中间件：

// src/middlewares/request-id.middleware.ts
import { Injectable, NestMiddleware } from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';
import { v4 as uuidv4 } from 'uuid';
import { asyncLocalStorage } from '../utils/async-local-storage';

@Injectable()
export class RequestIdMiddleware implements NestMiddleware {
  use(req: Request, res: Response, next: NextFunction) {
    const requestId = uuidv4();
    asyncLocalStorage.run({ requestId }, next);
  }
}

3. 在钩子中获取请求ID：

import { asyncLocalStorage } from '../utils/async-local-storage';

UserSchema.pre(/.*/, async function() {
  const store = asyncLocalStorage.getStore();
  const requestId = store?.requestId;
  this.startTime = Date.now();
  console.log(`Pre - Request id: ${requestId}`);
});

UserSchema.post(/.*/, function() {
  const store = asyncLocalStorage.getStore();
  const requestId = store?.requestId;
  const duration = Date.now() - this.startTime!;
  console.log(`Post - Request id: ${requestId}, 耗时: ${duration}ms`);
});

内容的提问来源于stack exchange，提问作者Roy Leibovitz