Unable to get mysql count in node.js route

user_6698796 0
Viewed 36

I am new to node.js, and currently working on demo project so my requirement is to get count of userId which I am calling by function and this function is declared outside of route, but I am getting undefined but in same function getting count values but when I returned count still getting undefined in route.

Code:

var express = require('express');
var router = express.Router();

router.get('/', function(req, res, next) {      
    const usersQuery = "SELECT * FROM users";
    dbConn.query(usersQuery,function(err,rows)     {
        if(err) {
            console.log('this error',res);
        } else {
            let total=getCount();   // calling function placed outside
            console.log(total);
            }
        
        });
    });

Function declared outside to return count:

function getCount(){
    const usersQuery = "SELECT count(id) as cnt FROM users";
    dbConn.query(usersQuery,function(err,rows)     {
        if(err) {
            console.log('failed  to get count');
        } else {
            return rows; // retun count 
          
            }
    })
}
express node.js mysql javascript
3 Answers

You need to return the result of the query

function getCount(){
    const usersQuery = "SELECT count(id) as cnt FROM users";
    return dbConn.query(usersQuery,function(err,rows)     {
        if(err) {
            console.log('failed  to get count');
        } else {
            return rows; // retun count
        }
    })
}

Note that probably returns a Promise you need to handle correctly.

user_58118740

Finally I got the required output by using Promise() in node js

Code:

var express = require('express');
var router = express.Router();

router.get('/', function(req, res, next) {      
    const Query = "SELECT * FROM t1";
    dbConn.query(Query,function(err,rows)     {
        if(err) {
            // write some code
        } else {
// call to promise
              getData().then(function (outputVal) {
                console.log(outputVal[0].Usr);
            }).catch(function () {
                // write error here
            });
        }
    
    });
});

// Promise code

function getData() {
    return new Promise(function (resolve, reject) {
        //  setTimeout(function () {
        const MQuery = "SELECT count(id) as Usr FROM t2";
        dbConn.query(MQuery , function (err, rows) {
            if (err) {
                reject();
            } else {
                resolve(rows);
            }
            // }, 1000);
        })
    })
}
user_66987960

A couple of things you should know:

  1. The functions declared outside routes will be executed first in stack once the server starts even though you haven't called the specific route yet. By the time you call this function, it already holds undefined or null depending on the code inside the functions.
  2. dbConn.query() is Promise. Which means it works synchronously.

if you need count of users, here is what you can do:

router.get('/', function(req, res, next) {      
    const usersQuery = "SELECT * FROM users";
    dbConn.query(usersQuery,function(err,rows)     {
        if(err) {
            console.log('this error',res);
        } else {
            let total= rows.length // you will get an array of users, therefore the number of users is equal to the length of the array
            console.log(total);
        }
        
   });
});
user_88527200
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