所以我看到了这篇精彩的帖子Error: Can't set headers after they are sent to the client,但仍然不明白,我的标题部分出了什么问题,因为当我将commented out
错误类型更改为两个独立的部分时:
app.use(doesNotModifyBody);
app.use(doesModifyBody);
(如上面的回答)它无法正常工作。
目前,我总是从app.use(doesModifyBody);
- res.write("<p>Hello World</p>");
重新获取字符串,而不是接收正确的数据库答案。
所以问题是,如何使用问题标题中的标题来解决错误,并使正确的数据库回答收到,而不是res.write("<p>Hello World</p>");
P.S。删除res.write("<p>Hello World</p>");
并不能解决问题。
我的服务器代码:
'use strict'
const express = require('express');
const mongoose = require('mongoose');
const bodyParser = require('body-parser');
const app = express();
const router = express.Router();
const EmployersSchemaDB = require('./SchemaDB/EmployersSchemaDB');
mongoose.connect('mongodb://myDB');
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
// app.use((req, res, next) => {
// res.setHeader('Access-Control-Allow-Origin', '*');
// res.setHeader('Access-Control-Allow-Credentials', 'true');
// res.setHeader('Access-Control-Allow-Methods', 'GET,POST,PUT,DELETE');
// res.setHeader('Access-Control-Allow-Headers', 'Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers');
// res.setHeader('Cache-Control', 'no-cache');
// next();
// }); I change this on:
let doesNotModifyBody = (req, res, next) => {
res.setHeader('Access-Control-Allow-Origin', '*');
res.setHeader('Access-Control-Allow-Credentials', 'true');
res.setHeader('Access-Control-Allow-Methods', 'GET,POST,PUT,DELETE');
res.setHeader('Access-Control-Allow-Headers', 'Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers');
res.setHeader('Cache-Control', 'no-cache');
next();
}; // this
let doesModifyBody = (req, res, next) => {
res.setHeader("Content-Type", "text/html");
res.write("<p>Hello World</p>");
res.end();
}; // and this
app.use(doesNotModifyBody);
app.use(doesModifyBody);
router.get('/', (req, res) => {
res.json({ message: 'Server is Initialized!'});
});
router.route('/employers')
.get((req, res) => {
EmployersSchemaDB.find((err, employers) => {
if (err) { res.send(err) }
res.json(employers);
});
})
.post((req, res) => {
let employer = new EmployersSchemaDB();
employer.first_name = req.body.first_name;
employer.last_name = req.body.last_name;
employer.birth_date = req.body.birth_date;
employer.salary = req.body.salary;
employer.save((err) => {
if (err) { res.send(err) }
res.json({ message: 'Comment successfully added!', employer });
console.log('---===--- \n Employer added: \n', employer + '\n ---===---');
});
});
router.route('/employers/:employer_id')
.get((req, res) => {
EmployersSchemaDB.findById(req.params.employer_id, (err, employer) => {
if (err) { res.send(err) }
res.json({ message: 'Employer has been getted', employer: employer });
});
})
.put((req, res) => {
EmployersSchemaDB.findById(req.params.employer_id, (err, employer) => {
if (err) { res.send(err) }
(req.body.id) ? employer.id = req.body.id : null;
(req.body.first_name) ? employer.first_name = req.body.first_name : null;
(req.body.last_name) ? employer.last_name = req.body.last_name : null;
(req.body.birth_date) ? employer.birth_date = req.body.birth_date : null;
(req.body.salary) ? employer.salary = req.body.salary : null;
employer.save((err) => {
if (err) { res.send(err) }
res.json({ message: 'Employer has been updated', employer: employer });
});
});
})
.delete((req, res) => {
EmployersSchemaDB.remove({ _id: req.params.employer_id }, (err, employer) => {
if (err) { res.send(err) }
res.json({ message: 'Comment has been deleted' })
})
});
app.use('/', router);
const port = process.env.API_PORT || 3016;
app.listen(port, () => {
console.log(`Server running on port ${port}`);
});
答案 0 :(得分:0)
问题是你正在打电话
res.write("<p>Hello World</p>");
res.end();
将响应发送回客户端。执行此操作后,您无法发送任何进一步的数据。您尝试通过调用中间件中的res.json()
来执行此操作,这就是您希望得到错误的原因;
同时删除res.end
和res.write
行,它应该可以正常工作。