无法在我的Node.js中附加res.send(result)以将数据发送到angular应用程序 [英] Unable to attach an res.send(result) in my Nodejs to send data to angular app

问题描述

我制作了一个Nodejs和angular2应用程序，需要将它们集成到Neo4j应用程序中.我可以从来自Angular2的NodeJS代码中访问数据库，但是后来我无法将该数据发送回angular2应用程序.如果我给

I have made a Nodejs and angular2 app where i need to integrate them to Neo4j app. I am able to hit the Database from my NodeJS code coming from Angular2 but then i am unable to send that data back to angular2 app. If i give

 res.send(result) 

在函数tmsServer的任何地方，都会出现错误->

anywhere in my function tmsServer , i get error -->

 inside catch = Error: Can't set headers after they are sent.

请帮助.我想将数据发送回角度应用程序.

Please help. I want to send my data back to angular app.

tmservercontroller.js

   // Require Neo4j
   var neo4j = require('neo4j-driver').v1;

  var path = require('path');
  var logger = require('morgan');
  var bodyParser = require('body-parser');
  var express = require('express');

  var router = express.Router();

   var app = express();


  // Create Driver
   const driver = new neo4j.driver("bolt://localhost:11001", 
   neo4j.auth.basic("neo4j", "Virtuallib1"));



 // //View Engine

   app.set('views', path.join(__dirname, 'views'));

   app.use(logger('dev'));
    app.use(bodyParser.json());
    app.use(bodyParser.urlencoded({ extended: false }));
    app.use(express.static(path.join(__dirname, 'public')));



  var session = driver.session();
  var request = require('request');

   var finalResult ;

   router.post('/', tmsServer);
   module.exports = router;


   function tmsServer(req, res) { 

    session
       .run('MATCH (n) RETURN n LIMIT 5')

       .then(function (result){

           result.records.forEach(function(record){
               console.log("record = ", record);
               console.log("result = ", result)
               console.log("1] 
   record._fields[0].properties=",record._fields[0].properties);


                    res.send(result); 
           });


       })


       .catch(function(err){
        console.log("inside catch = "+err);
    })

    res.send('It Works');
    session.close();
   }

neo4j-primary.component.ts

   import { Component, OnInit } from '@angular/core';
   import { Injectable } from '@angular/core';

 import { ToasterService } from '../toaster.service';

  import { FormGroup, FormControl, FormBuilder, Validators } from 
 '@angular/forms';
   import { Http, Response, Headers } from '@angular/http';
  import { config } from '../config';
  import { Subject } from 'rxjs';

  import 'rxjs/add/operator/map';
  import { map } from 'rxjs/operators';
  import 'rxjs/Rx';
  import { Observable } from 'rxjs';

  // Statics
  import 'rxjs/add/observable/throw';


 @Component({
  selector: 'app-neo4j-primary',
  templateUrl: './neo4j-primary.component.html',
  styleUrls: ['./neo4j-primary.component.css']
  })

 export class Neo4jPrimaryComponent implements OnInit {

 constructor(private http: Http,  private notify: ToasterService) { }

 ngOnInit() {
this.viewNodesStart();
    }


  emptyObj1;
   emptyObj;
   info;

   // -------------------------------  Nodes Entire Data -------------

  viewNodesStart() {

console.log("INSIDE viewNodesStart()")

// Nodes Value

   console.log("inside Nodes Value");
  var data = localStorage.getItem('token');

 console.log("data is=>",data+ "emptyobj1 = "+ this.emptyObj1);

   var url = config.url;
   var port = config.port;

   var object = {
    "emptyObj" : this.emptyObj
    }
    this.http.post("http://" + url+":" + port + 
    "/viewNodesStart",this.emptyObj1)
  .map(Response => Response)
  .subscribe((res: Response) => {

    console.log("XXXXXXXXXXXX Response on /viewNodesStart", res);

    this.info = res;   

    if (this.info.statusCode == 200) {
      console.log("Data added successfully");

    } else {
      console.log("Data is not inserted")

     }
     });

   }

   }

推荐答案

您只能将响应发送回一次，在发送响应它有效"的同时运行异步操作，然后再次发送包含实际数据的响应.

You can send the response back ONLY once, you have an asynchronous operation running while you send the response "It works" and again sending the response with actual data.

res.send将响应标头设置为对象，该对象应该在请求生命周期中理想发生一次.

res.send sets response headers to object which should ideally happen once during the request lifecycle.

function tmsServer(req, res) { 
    session
     .run('MATCH (n) RETURN n LIMIT 5')
     .then(function (result){
       result.records.forEach(function(record){
         // This will execute only when the promise is resolved and data is returned from database.
         res.send(result); // (RES02)
       });
     })
     .catch(function(err){
      console.log("inside catch = "+err);
     })

     res.send('It Works'); // (RES01) <--- This runs before RES02
    session.close();
}

您的答案的解决方案是删除RES01.

The solution to your answer is to remove RES01.

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