无法在 Nestjs 的 WebSocket 侦听器中调用服务

Question

我已经使用下面的方法在 Nestjs 中实现了 WebSockets，其中一个要求是，一旦我从 websocket 服务器收到任何消息，我需要更新数据库。 为了做到这一点，我已经完成了下面的代码，但得到了这样的错误：

但是，如果我在任何其他控制器方法中调用相同的方法，它就可以正常工作（检查 /test1）。只有当我从 websocket 侦听器调用它时，我才会收到此错误。即使我从同一个控制器调用简单的方法来打印一些日志，我也会收到相同的错误 TypeError: this.processData is not a function。奇怪！

谁能告诉我我做错了什么？

(node:11421) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'updateResponseData' of undefined
    at WebSocket.incoming (/opt/dist/controller/sample.controller.js:62:44)
    at WebSocket.emit (events.js:210:5)
    at Receiver.receiverOnMessage (/opt/node_modules/ws/lib/websocket.js:800:20)
    at Receiver.emit (events.js:210:5)
    at Receiver.dataMessage (/opt/node_modules/ws/lib/receiver.js:423:14)
    at Receiver.getData (/opt/node_modules/ws/lib/receiver.js:353:17)
    at Receiver.startLoop (/opt/node_modules/ws/lib/receiver.js:139:22)
    at Receiver._write (/opt/node_modules/ws/lib/receiver.js:74:10)
    at doWrite (_stream_writable.js:431:12)
    at writeOrBuffer (_stream_writable.js:415:5)
    at Receiver.Writable.write (_stream_writable.js:305:11)
    at Socket.socketOnData (/opt/node_modules/ws/lib/websocket.js:875:35)
    at Socket.emit (events.js:210:5)    
    at addChunk (_stream_readable.js:308:12)
    at readableAddChunk (_stream_readable.js:289:11)
    at Socket.Readable.push (_stream_readable.js:223:10)
(node:11421) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:11421) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

控制器代码：

import { Controller, Post, Get, Inject, Req, UsePipes, Body, Header,Param } from '@nestjs/common';
import { Request } from 'express';
import * as WebSocket  from 'ws';
import { DatabaseService } from '../service/datafetch.service';

@Controller('sample')
export class SampleController {

    @Inject(dbService)
    private dbService: DatabaseService;

    static ws: any;
    static wsnew: any;
    public receiveDistData = '';

    // Connect WS & Listen to messages
    constructor() {
        this.initWs();     

        SampleController.ws.on('message', async function incoming(data) {
            console.log('message recieved 8081');
            var dataJson = JSON.parse(data);
            await this.dbService.updateResponseData(dataJson);
            return data;       
        }); 
    }

    @Get('/test/data/:id')
    async testData(@Param('id') id: string) {
        return await this.callWs(id);
    }

    @Get('/test1/data/:id')
    async testData1(@Param('id') id: string) {
        const data = {id: id, data:{}};
        return await this.dbService.updateResponseData(data);
    }

    async initWs() {
        SampleController.ws = new WebSocket('ws://127.0.0.1:8081');
    }

    async processData() {
        console.log('Printing a log...');
    }

    // Data Distribution
    async callWs(id) {    
        // If Socket is not opened, try to re-open    
        if(SampleController.ws.readyState != 1) { 
            console.log('Server is dead....');
            this.initWs();
        }

        const Data = await this.dbService.findAll(id);
        await SampleController.ws.send(JSON.stringify({
            event: 'channel1',
            data: Data,
        }));
    }

}

存储库代码：

import { InjectRepository } from '@nestjs/typeorm';
import { Injectable } from '@nestjs/common';
import { Repository } from 'typeorm';
import { SampleRepository } from '../repository/sample.repository';

@Injectable()
export class SampleService {

  constructor(
    @InjectRepository(SampleRepository)
    private readonly sampleRepository: SampleRepository
  ) {}

  async updateResponseData(data): Promise<any> {
    return await this.sampleRepository.updateData(data);
  }

}

Answer 1

在匿名函数中，this 指的是全局对象，而不是您的服务实例。

相反，您可以使用箭头函数。在这里，this 指的是类实例，正如您所期望的那样：

async function(data) {
  // this is global object
  this.call();


(data) => {
  // this is the same as in enclosing object
  this.call();