nodejs: 能否从被调用的函数中使用 res.send()？

huangapple
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英文:

nodejs: can res.send() be done from a called function?

问题

I'm new to Node.JS and I'm trying to write an API which stores user data in a database after checking if the username already exists.
Below is my app.js code

  1. const http = require('http');
  2. const express = require('express');
  3. const bodyParser = require('body-parser');
  4. const app = express();
  5. const sqlHelper = require('./sqlHelper');
  7. app.use(bodyParser.json());
  9. app.post('/registeruser',(req,res)=>{
  10.     const userName = req.body.username;
  11.     const password = req.body.password;
  12.     const firstName = req.body.firstname;
  13.     const lastName = req.body.lastname;
  14.     const userDetail = {
  15.         userName,
  16.         password,
  17.         firstName,
  18.         lastName
  19.     }
  20.     sqlHelper.addUserSQL(userDetail,res);
  21.     res.send("User Registerd Seccesfuly");
  22. })
  24. const server = http.createServer(app);
  25. server.listen(3000);

Below is my sqlHelper.js code

  1. const mysql = require('mysql2');
  3. const addUserSQL = (userDetail,res) => {
  4.     const con = mysql.createConnection({
  5.         host:'localhost',
  6.         user:'root',
  7.         password:'mysqlpw',
  8.         multipleStatements: true
  9.     });
  10.     con.connect(function(err){
  11.         if(err)
  12.             throw err
  13.         console.log("CHECKING IF USER ALREADY EXIST");
  14.         let sql = `USE mydatabase; SELECT * FROM usertable WHERE username=?`;
  15.         con.query(sql,[userDetail.userName],function(err,result){
  16.             if(err)
  17.                 throw err;
  18.             if(result[1]!=[]){
  19.                 res.send("ERROR: USERNAME ALREADY EXISTS");
  20.             }
  21.         })
  22.     })
  24. }
  26. module.exports={addUserSQL};

When there is a request with a username that is already in my database I get the following response User registered successfully instead of ERROR: USERNAME ALREADY EXISTS and a error in terminal
Cannot set headers after they are sent to the client.
How can I write this code in a proper way to check if a username already exists and send a response back?

英文:

I'm new to Node.JS and I'm trying to write an API which stores user data in a database after checking if the username already exists.
Below is my app.js code

  1. const http = require('http');
  2. const express = require('express');
  3. const bodyParser = require('body-parser');
  4. const app = express();
  5. const sqlHelper = require('./sqlHelper');
  8. app.use(bodyParser.json());
  10. app.post('/registeruser',(req,res)=>{
  11.     const userName = req.body.username;
  12.     const password = req.body.password;
  13.     const firstName = req.body.firstname;
  14.     const lastName = req.body.lastname;
  15.     const userDetail = {
  16.         userName,
  17.         password,
  18.         firstName,
  19.         lastName
  20.     }
  21.     sqlHelper.addUserSQL(userDetail,res);
  22.     res.send("User Registerd Seccesfuly");
  23. })
  26. const server = http.createServer(app);
  27. server.listen(3000);

Below is my sqlHelper.js code

  1. const mysql = require('mysql2');
  3. const addUserSQL = (userDetail,res) => {
  4.     const con = mysql.createConnection({
  5.         host:'localhost',
  6.         user:'root',
  7.         password:'mysqlpw',
  8.         multipleStatements: true
  9.     });
  10.     con.connect(function(err){
  11.         if(err)
  12.             throw err
  13.         console.log("CHECKING IF USER ALREADY EXIST");
  14.         let sql = `USE mydatabase; SELECT * FROM usertable WHERE username=?`;
  15.         con.query(sql,[userDetail.userName],function(err,result){
  16.             if(err)
  17.                 throw err;
  18.             if(result[1]!=[]){
  19.                 res.send("ERROR: USERNAME ALREADY EXISTS");
  20.             }
  21.         })
  22.     })
  24. }
  26. module.exports={addUserSQL};

When there is a request with a username that is already in my database I get the following response User registered successfully instead of ERROR: USERNAME ALREADY EXISTS and a error in terminal
Cannot set headers after they are sent to the client.
How can I write this code in a proper way to check if a username already exists and send a response back?

答案1

得分: 0

A straight answer to your question is NO.

You should never do res.send from a function being called.

Instead, you should return an error from your sqlhelper code.

Try this code:

  1. app.post('/registeruser', async (req, res) => {
  2.     const userName = req.body.username;
  3.     const password = req.body.password;
  4.     const firstName = req.body.firstname;
  5.     const lastName = req.body.lastname;
  6.     const userDetail = {
  7.         userName,
  8.         password,
  9.         firstName,
  10.         lastName
  11.     }
  12.     const { err } = await sqlHelper.addUserSQL(userDetail);
  13.     if (err) return res.status(500).send(err);
  14.     res.send("User Registered Successfully");
  15. })

Changes in sqlHelper file:

  1. const mysql = require('mysql2/promise');
  3. const options = {
  4.     host: 'localhost',
  5.     user: 'root',
  6.     password: 'mysqlpw',
  7.     multipleStatements: true
  8. };
  10. const addUserSQL = async (userDetail) => {
  11.     const connection = await mysql.createConnection(options);
  12.     const query = `USE mydatabase; SELECT * FROM usertable WHERE username=?`;
  13.     const [rows, fields] = await connection.execute(query, [userDetail.userName]);
  15.     if (rows?.length > 0) {
  16.         return { err: "ERROR: USERNAME ALREADY EXISTS" };
  17.     } else {
  18.         // Code to create a user entry in your db
  19.     }
  20. }
  22. module.exports = { addUserSQL };
英文:

A straight answer your question is NO

You should never do res.send from function being called.

Instead,You should return error from your sqlhelper code.

Try this code:

  1. app.post('/registeruser',async (req,res)=>{
  2.     const userName = req.body.username;
  3.     const password = req.body.password;
  4.     const firstName = req.body.firstname;
  5.     const lastName = req.body.lastname;
  6.     const userDetail = {
  7.         userName,
  8.         password,
  9.         firstName,
  10.         lastName
  11.     }
  12.     const {err} = await sqlHelper.addUserSQL(userDetail);
  13.     if(err) return res.status(500).send(err);
  14.     res.send("User Registerd Seccesfuly");
  15. })

Changes in sqlHelper file:

  1. const mysql = require('mysql2/promise');
  3. const options = {
  4.     host:'localhost',
  5.     user:'root',
  6.     password:'mysqlpw',
  7.     multipleStatements: true
  8. };
  10. const addUserSQL =async (userDetail) => {
  11.     const connection = await mysql.createConnection(options);
  12.     const query = `USE mydatabase; SELECT * FROM usertable WHERE username=?`;
  13.     const [rows, fields] = await connection.execute(query, [userDetail.userName]);
  15.     if(rows?.length>0){
  16.        return {err: "ERROR: USERNAME ALREADY EXISTS" };
  17.     }else{
  18.       //code to create user entry in your db
  19.     }
  20. }
  22. module.exports={addUserSQL};

huangapple
  • 本文由 发表于 2023年1月5日 20:01:26
  • 转载请务必保留本文链接：https://go.coder-hub.com/75018077.html
  • express
  • node.js
  • sql
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