我正在尝试使用Angular在MongoDB中添加新条目。我无法摆脱以下错误消息。有任何想法吗？先感谢您！

（注意：与数据库的连接是正常的。例如，我的get（）函数正在工作）

错误消息

C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\mongodb\lib\utils.js:123
    process.nextTick(function() { throw err; });
                                  ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:470:11)
    at ServerResponse.header (C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\express\lib\response.js:725:10)
    at ServerResponse.send (C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\express\lib\response.js:170:12)
    at ServerResponse.json (C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\express\lib\response.js:256:15)
    at db.get.collection.insert (C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\routes\api.js:22:21)
    at C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\mongodb\lib\collection.js:525:20
    at C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\mongodb\lib\collection.js:659:14
    at handleCallback (C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\mongodb\lib\utils.js:120:56)
    at resultHandler (C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\mongodb\lib\bulk\ordered.js:421:14)
    at C:\Server Files\112-IT-Dep-Equipment-Registering (Back-end)\node_modules\mongodb-core\lib\connection\pool.js:461:18

服务器中的API

//----- Add a new entry -----
router.post('/addNewEntry',(req,res,next) => {
    var newEntry = req.body;
    db.get().collection('data')
            .insert(newEntry,(err,data) => {
                if (err) { res.send(err) }
                res.json({status: 'OK'});
            });
});

“入门”课程

export class Entry {
    _id: string;
    equipment: string;
    model: string;
    serial: string;
    network: string;
    ip: string;
    description: string;
    office: string;
}

entry.service.ts

import { Injectable }                                 from '@angular/core';
import { HttpClient,HttpErrorResponse,HttpHeaders } from '@angular/common/http';
import { throwError }                                 from 'rxjs';
import { catchError,retry }                          from 'rxjs/operators';
import { Entry }                                      from '../Classes/entry';

const httpoptions = {
  headers: new HttpHeaders({
    'Content-Type':  'application/json'
  })
};

@Injectable()
export class EntryService {

    constructor(private http: HttpClient) { }

    // ----- Add a new entry -----
    addNewEntry(newEntry: Entry) {
        return this.http
                   .post<Entry>('http://192.168.1.5:3000/api/addNewEntry',newEntry,httpoptions)
                   .pipe(catchError(this.handleError));
    }

} // end of Service

app.component.ts

addNewEntry(): void {
        this.entryService
            .addNewEntry(this.newEntry)
            .subscribe(res => {
                this.newEntry = { _id: '',equipment: '',model: '',serial: '',network: '',ip: '',description: '',squadron: '',office: '' };
                this.success = true;
            },err => {
              this.errorMsg = err;
              this.error = true;
            });
    }