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Node.js MongoDB '.then' throws 'ERR_HTTP_HEADERS_SENT' error(Node.js MongoDB“.then”抛出“ERR_HTTP_HEADERS_SENT”错误)

转载 作者：bug小助手 更新时间：2023-10-22 15:15:31 28 4
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I'm doing mongodb database after tutorial from NetNinja. Since I'm kinda bad with js, I'm just following his actions. I'm stuck with:

在NetNinja的教程之后，我正在做mongodb数据库。因为我对js有点不好，所以我只是关注他的行为。我被困在：


node:internal/errors:496
    ErrorCaptureStackTrace(err);
    ^
...
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client


I'm having only 2 files:
app.js

我只有两个文件：app.js


const express = require('express')
const { connectToDb, getDb} = require('./db')

const app = express()

let db

connectToDb((err) => {
    if(!err) {
        app.listen(3000, () => {
            console.log('app listening on port 3000')
        })
        db = getDb()
    }
})

app.get('/books/books', (req, res) => {
    let books = []

    db.collection('books')
        .find()
        .sort({ author: 1 })
        .forEach(book => books.push(book))
        .then(() => {
            res.status(200).json(books)
        })
        .catch(() => {
            res.status(500).json({error : 'Could not fetch the documents'})
        })

    res.json({mssg: "welcome to the api"})
})

db.js

db.js


const { MongoClient } = require('mongodb')

let dbConnection

module.exports = {
    connectToDb: (cb) => {
        MongoClient.connect('mongodb://0.0.0.0:27017/bookstore')
            .then((client) => {
                dbConnection = client.db()
                return cb()
            })
            .catch(err => {
                console.log(err)
                return cb(err)
            })
    },
    getDb: () => dbConnection
}


I found the place that throws me this error, when I'm removing it, there's no error:
app.js, app.get block

我找到了引发这个错误的地方，当我删除它时，没有错误：app.js，app.get块


.then(() => {
            res.status(200).json(books)
        })

Since NetNinja has no problems, error could be triggered by different versions of Node, but I dunno for sure.
Is there a replacement to '.then', that'll let me use database?

由于NetNinja没有问题，不同版本的Node可能会触发错误，但我不确定。有没有替代“.then”的方法，可以让我使用数据库？


更多回答
优秀答案推荐

The error in the code you provided is that you're sending a response (res.json({mssg: "welcome to the api"})) after making a database query. In Node.js and Express, the response should only be sent once. When you send a response, you can't send another one.

您提供的代码中的错误是，您在进行数据库查询后发送了一个响应（res.json（{mssg:“欢迎使用api”}）。在Node.js和Express中，响应应该只发送一次。发送响应时，无法再发送另一个响应。



This error does not occur because of the node version or .then its occuing because you are sending a response 2 time

此错误不是因为节点版本而发生的，或者。然后是因为您发送了2次响应而引起的


Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

First:

第一：


res.json({mssg: "welcome to the api"});

Second:

第二：


res.status(200).json(books);

Fix:

修复：


just remove the second response

只需删除第二个响应


app.get('/books/books', (req, res) => {
    let books = []

    db.collection('books')
        .find()
        .sort({ author: 1 })
        .forEach(book => books.push(book))
        .then(() => {
            res.status(200).json(books)
        })
        .catch(() => {
            res.status(500).json({error : 'Could not fetch the documents'})
        })

    
})

更多回答

that worked, thank you

起作用了，谢谢

Kindly mark this answer as the correct one. Thanks!

请把这个答案标记为正确答案。谢谢

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