Angular Node.js:输出未定义,无法从服务器访问数据

时间:2018-12-29 06:55:03

标签: node.js angular rxjs

我刚刚开始在Node和Angular中进行编程,并且试图运行一个简单的应用程序,其中将后端(localhost:3000)连接到前端并显示数据。如果发出请求时我从服务器收到的数据放在一个.json文件中,而我在同一文件夹中访问它,则该数据将被显示。

但是,如果我使用从中选择了数据的api(http:// localhost:3000 / purchase)的地址,则会在浏览器中收到未定义的错误。

这是浏览器中显示的错误:

ContactsComponent.html:2 ERROR TypeError: Cannot read property 'Empno' of undefined
    at Object.eval [as updateRenderer] (ContactsComponent.html:2)
    at Object.debugUpdateRenderer [as updateRenderer] (core.js:22503)
    at checkAndUpdateView (core.js:21878)
    at callViewAction (core.js:22114)
    at execComponentViewsAction (core.js:22056)
    at checkAndUpdateView (core.js:21879)
    at callViewAction (core.js:22114)
    at execComponentViewsAction (core.js:22056)
    at checkAndUpdateView (core.js:21879)
    at callWithDebugContext (core.js:22767)

这是我的服务器(http://localhost:3000/purchase)在Postman上的输出:

{
    "Empno": "113       ",
    "Ename": "Mary      ",
    "Sal": "15220     ",
    "Deptno": "DP        "
}

这是该服务的相应代码:

import { Injectable } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpClient } from '@angular/common/http';
import 'rxjs/add/operator/map';
import { map, filter, switchMap, catchError } from 'rxjs/operators';
import { Contact } from './contact';
import { HttpErrorResponse, HttpResponse } from '@angular/common/http';
import { Observable, throwError } from 'rxjs';
import { retry } from 'rxjs/operators';



@Injectable({
  providedIn: 'root'
})

export class ContactService {
  contact: Contact[];
  //  configUrl1 = '../assets/test.json';
 configUrl1 = 'http://localhost:3000';


  constructor(private http: HttpClient) { }
  // retrieving contacts

  getPurchase() {
    return this.http.get(this.configUrl1);
  }

}

**This is the code for the Component:**

import { Component, OnInit } from '@angular/core';
import {  ContactService } from '../contact.service';
import { Contact } from '../contact';


@Component({
  selector: 'app-contacts',
  templateUrl: './contacts.component.html',
  styleUrls: ['./contacts.component.scss'],
  providers: [ContactService]
})
export class ContactsComponent implements OnInit {
  contact: Contact;
  Empno: string;
    Ename: string;
    Sal: string;
    Deptno: string;


  constructor(private contactService: ContactService) { }

  ngOnInit() {
    this.contactService.getPurchase()
      .subscribe((data: Contact) => this.contact = {...data});
    }

}

这是用于定义联系人结构的代码:

export class Contact {
    Empno: string;
    Ename: string;
    Sal: string;
    Deptno: string;
    }

这是联系人组件的HTML文件的代码:

<div class= "container">
  <p>Its Working here also</p>

    {{contact.Empno}}
    {{contact.Ename}}

</div>

服务器端代码: App.js

//importing modules
var express = require('express');
var bodyParser = require('body-parser');
var cors = require('cors');
var mssql = require('mssql');
var path = require('path');
var app = express();

const route = require('./routes/route');
//port no
const port = 3000;

// adding middlewear - cors
app.use(cors());

// adding middlewear - bodyparser
// app.use(bodyparser.json());

// static files
app.use(express.static(path.join(__dirname, 'public')));

//creating routes
app.use('/purchase', route);

//testing 
app.get('/', (req,res)=>{
    res.send('foobar');
});

// //bind the port
app.listen(port, () => {
  console.log('Server started at port: ' + port);
});

// create application/json parser
var jsonParser = bodyParser.json()
// app.use(bodyParser.json({ type: 'application/*+json' }))

// POST /login gets urlencoded bodies
app.post('/login', jsonParser, function (req, res) {
  if (!req.body) return res.sendStatus(400)
  res.send('welcome, ' + req.body.username)
})

route.js

const express = require('express');
const router = express.Router();
var bodyParser = require('body-parser');
var app = express();
const sql = require('mssql');
const config = 'mssql://vpn:vpn1@ASPL-AVG:1433/Sampledb';


app.use(bodyParser.json());

var jsonParser = bodyParser.json()

router.get('/', jsonParser,(req,res, next)=>{
  var conn = new sql.ConnectionPool(config);
  conn.connect().then((conn) => {
    var sqlreq = new sql.Request(conn);
    sqlreq.execute('SelEmpl10', function(err, recordset) {
      res.json(recordset.recordsets[0][1]);
      console.log(recordset.recordsets[0][1]); 

    })
    })
  });

//add purchase order
router.post('/' , jsonParser ,(req, res, next) => {
    //logic to add record
    console.log(req.body.username);
    var conn = new sql.ConnectionPool(config);
    conn.connect().then((conn) => {
      var sqlreq = new sql.Request(conn);
      sqlreq.input('Username', sql.VarChar(30), req.body.username);
      sqlreq.input('Password', sql.VarChar(30), req.body.password);
      sqlreq.input('Email', sql.VarChar(30), req.body.email);
      sqlreq.input('Name', sql.VarChar(30), req.body.name);
      sqlreq.execute('saveuser').then(function(err, recordsets, returnValue, affected) {
        console.dir(recordsets);
        console.dir(err);
        conn.close();
      }).catch(function(err) {
            res.json({msg: 'Failed to add contact'});
            console.log(err);
      });
    });
  })



//delete purchase order
router.delete('/:id', (req, res, next) => {
    //logic to delete record

});

module.exports = router;  

从SQL接收的数据是这样的:

{
    "recordsets": [
        [
            {
                "Empno": "112       ",
                "Ename": "john      ",
                "Sal": "142500    ",
                "Deptno": "CS        "
            },
            {
                "Empno": "113       ",
                "Ename": "Mary      ",
                "Sal": "15220     ",
                "Deptno": "DP        "
            }
        ]
    ],
    "recordset": [
        {
            "Empno": "112       ",
            "Ename": "john      ",
            "Sal": "142500    ",
            "Deptno": "CS        "
        },
        {
            "Empno": "113       ",
            "Ename": "Mary      ",
            "Sal": "15220     ",
            "Deptno": "DP        "
        }
    ],
    "output": {},
    "rowsAffected": [
        2
    ],
    "returnValue": 0
}

在Node中添加参数后,输出为:

{
    "Empno": "113       ",
    "Ename": "Mary      ",
    "Sal": "15220     ",
    "Deptno": "DP        "
}

2 个答案:

答案 0 :(得分:0)

contact变量添加安全的导航操作。

<div class= "container">
  <p>Its Working here also</p>
    {{contact?.Empno}}
    {{contact?.Ename}}
</div>

等效于contact != null ? contact.Empno: null

更新:

此外,添加错误处理代码:

ngOnInit() {
  this.contactService.getPurchase().subscribe(
    (data: Contact) => {
      this.contact = {...data};
    },
    error => {
      console.log("Error Occured: "+ error);
    }
  );
}

答案 1 :(得分:0)

该问题可能与使用bodyParser有关。它可能正在尝试解析已解析的JSON。基本上在顶层添加一次解析器,然后将其从路由中删除。也可以使用json()代替send()来连接它。我遇到的问题是,如果数据具有名为data的属性,则可能导致json parse / stringify失败。

尝试以下方法。在App.js中重新引入行app.use(bodyParser.json()),只需在顶级条目(例如此条目文件)中添加一次即可。同样从此文件中,从jsonParser POST路由中删除/login中间件:

var bodyParser = require('body-parser');
var app = express();

const route = require('./routes/route');
//port no
const port = 3000;

// adding middlewear - cors
app.use(cors());

// adding middlewear - bodyparser
app.use(bodyParser.json());

// static files
app.use(express.static(path.join(__dirname, 'public')));

//creating routes
app.use('/purchase', route);

//testing 
app.get('/', (req,res)=>{
    res.send('foobar');
});

// //bind the port
app.listen(port, () => {
  console.log('Server started at port: ' + port);
});

// POST /login gets urlencoded bodies
app.post('/login', function (req, res) {
  if (!req.body) return res.sendStatus(400)
  res.send('welcome, ' + req.body.username)
})

route.js中,删除bodyParser.json()jsonParser中间件,因为app.use(bodyParser.json());将其应用于所有路由,它已被包含在顶层。 /动词:

const express = require('express');
const router = express.Router();
var app = express();
const sql = require('mssql');
const config = 'mssql://vpn:vpn1@ASPL-AVG:1433/Sampledb';

router.get('/',(req, res, next)=>{
  var conn = new sql.ConnectionPool(config);
  conn.connect().then((conn) => {
    var sqlreq = new sql.Request(conn);
    sqlreq.execute('SelEmpl10', function(err, recordset) {
      res.json(recordset.recordsets[0][1]);
      console.log(recordset.recordsets[0][1]); 
    })
    })
  });

//add purchase order
router.post('/', (req, res, next) => {
    //logic to add record
    console.log(req.body.username);
    var conn = new sql.ConnectionPool(config);
    conn.connect().then((conn) => {
      var sqlreq = new sql.Request(conn);
      sqlreq.input('Username', sql.VarChar(30), req.body.username);
      sqlreq.input('Password', sql.VarChar(30), req.body.password);
      sqlreq.input('Email', sql.VarChar(30), req.body.email);
      sqlreq.input('Name', sql.VarChar(30), req.body.name);
      sqlreq.execute('saveuser').then(function(err, recordsets, returnValue, affected) {
        console.dir(recordsets);
        console.dir(err);
        conn.close();
      }).catch(function(err) {
            res.json({msg: 'Failed to add contact'});
            console.log(err);
      });
    });
  })

// delete purchase order
router.delete('/:id', (req, res, next) => {
    //logic to delete record
});

module.exports = router; 

如果仍然失败,请尝试仅使用res.send()而不是res.json(),甚至只是出于故障排除的目的。

最后我建议发送一个实际错误或至少某种类型的4xx5xx状态码,以便Angular HttpClient可以将其视为实际错误而不是成功。带有200状态代码的HTTP请求。

希望有帮助!