Why Variable is undefined in nodejs express

Question

I am using node js express and calling model from the controller.When I call model form controller and getting a result in result variable and print it in console.log(result) it's undefined.

Controller

var user_model=require('../models/user');

exports.get_user = function(req, res) {

    var result = user_model.get_users();

    console.log(result);
}

Model

var connection=require('../config/connection');

exports.get_users = function() {

    connection.query('SELECT * FROM users', function(err, rows) {
        if(err) {
            retrun err;
        }
        return rows;
    });
}

The problem is that the query result is being passed to a callback function, so the return rows; line will return the rows in the context of that function as opposed to the parent get_users function. — Mike Eason
– Mike Eason, Commented Feb 14, 2018 at 10:40
Possible duplicate of How do I return the response from an asynchronous call? — ponury-kostek
– ponury-kostek, Commented Feb 14, 2018 at 12:53

Virendra Yadav · Accepted Answer · 2018-02-14 10:59:40Z

1

This is happening because you are consoling the result before the query has finished. Node is asynchronous. Unlike php node doesn't wait for the query to finish before going to the next line.

answered Feb 14, 2018 at 10:59

Virendra Yadav

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3 Comments

Shubham Azad Over a year ago

then what i will do

Virendra Yadav Over a year ago

First thing is you can use promise for the same, but if you don't want to use promise then you can create method that will wait for the result i.e.

Virendra Yadav Over a year ago

Rahul Sharma · Accepted Answer · 2018-02-14 10:40:47Z

1

Use promise to handle async calls

// **Controller** 
var user_model = require('../models/user');

exports.get_user = function (req, res) {

    user_model.get_users().then((result) => {
        console.log(result);
    }).catch(err => console.log(err));
}

// **Model** 
var connection = require('../config/connection');
exports.get_users = function () {
    return new Promise((resolve, reject) => {
            connection.query('SELECT * FROM users', function (err, rows) {
                if (err) {
                    reject(err);
                }
                resolve(rows);
            });
        }
    })
}

answered Feb 14, 2018 at 10:40

Rahul Sharma

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