Question 20266 in Mysql Question posted in
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Error when retrieving data from SQL in nodejs – Mysql

I connected the database to the project in node js and the connection works without a problem, but when I try to retrieve the data using the get operation, an error occurs that I could not solve

sql connection

const mysql = require("mysql");
const connection = mysql.createConnection({
host: "localhost",
user: "root",
password: "my password",
database: "test"
});
connection.connect(function (err) {
if (err) throw err
    console.log("connection");
})
module.exports = { connection }

Request from the page

const express = require("express");
const {connection} = require('../../dbConected')
const router = express.Router();

const {
getallstudents
} = require('../controllers/student')
router.get("/", getallstudents)

module.exports = router;

controllers

const {connection} = require('../../dbConected')
module.exports = {
    getallstudents:
    connection.query("SELECT * FROM test.student",function (err,result){
        if (err) throw err;
        console.log(result);
    })
}

the error

Route.get() requires a callback function but got a [object Object]

and

[nodemon] app crashed – waiting for file changes before starting…

Thanks for the helpers

Tags:

3

Answers


  1. Chosen as BEST ANSWER
    0 
    const {connection} = require('../../dbConected')
module.exports = {
    getallstudents:(req, res) => {
       const select = connection.query("SELECT * FROM student")
       let json_select = JSON.stringify(select)
            res.status(200).json({
                json_select
            }).catch(error => {
            res.status(500).json({
                error
            })
        })
    }
}

    And I get an error in the json file the err

    "message": "Converting circular structure to JSONn --> starting at object with constructor 'Query'n | property '_timer' -> object with constructor 'Timer'n --- property '_object' closes the circle"

    and GET /getallstudents 500 2.939 ms - 224


  2. 0

    Main issue here is the router.get requires a function but in example there is a object instead of it. So ‘getallstudents’ must be a function.

    getallstudents:
connection.query("SELECT * FROM test.student",function (err,result){
    if (err) throw err;
    console.log(result);

    Change this to

    getallstudents: (function () => {
connection.query("SELECT * FROM test.student",function (err,result){
    if (err) throw err;
    console.log(result);
})(); //not sure about the last two parentheses
    Login or Signup to reply.
  3. 0

    You need to pass a callback which will be the controller for the router.get, RTM https://expressjs.com/en/guide/routing.html

    module.exports = {
    getallstudents: (req, res, next) => {
      // code here
    }
}

    then inside this code:

    connection.query("SELECT * FROM test.student",function (err,result){
  if (err) throw err;
  console.log(result);
})

    rather than doing if (err) throw err; console.log(result);, send the response back.

    connection.query("SELECT * FROM test.student",function (err,result) {
  if (err) {
    return next(err);
  }

  res.json(result);
})

    or like:

    module.exports = {
  getallstudents: async (req, res, next) => {
    try {
      res.json(await connection.query("SELECT * FROM test.student"))
    } catch (err) {
      next(err)
    }
  }
}

    ..but what is next(err), rtm: https://expressjs.com/en/guide/error-handling.html#writing-error-handlers

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