nodejs- unable to return result to controller function

Question

From my Model, I fetch some articles from a MySQL database for a user.

Model

var mysql = require('mysql');
var db = mysql.createPool({
    host: 'localhost',
    user: 'sampleUser',
    password: '',
    database: 'sampleDB'
});

fetchArticles: function (user, callback) {
    var params = [user.userId];
    var query = `SELECT * FROM articles WHERE userId = ? LOCK IN SHARE MODE`;
    db.getConnection(function (err, connection) {
        if (err) {
            throw err;
        }
        connection.beginTransaction(function (err) {
            if (err) {
                throw err;
            }
            return connection.query(query, params, function (err, result) {
                if (err) {
                    connection.rollback(function () {
                        throw err;
                    });
                }
                //console.log(result);
            });
        });
    });
}

This is working and the function fetches the result needed. But it's not returning the result to the controller function (I am returning it but I'm not able to fetch it in the controller function. I guess, I did something wrong here).

When I did console.log(result) this is what I got.

[ RowDataPacket {
    status: 'New',
    article_code: 13362,
    created_date: 2017-10-22T00:30:00.000Z,
    type: 'ebook'} ]

My controller function looks like this:

var Articles = require('../models/Articles');
exports.getArticle = function (req, res) {

    var articleId = req.body.articleId;
    var article = {
        userId: userId
    };

    Articles.fetchArticles(article, function (err, rows) {
        if (err) {
            res.json({ success: false, message: 'no data found' });
        }
        else {
            res.json({ success: true, articles: rows });
        }
    });
};

Can anyone help me figure out what mistakes I made here? I'm pretty new to nodejs. Thanks!

Answer 1

The simple answer is that you're not calling the callback function, anywhere. Here's the adjusted code:

fetchArticles: function (user, callback) {
    var params = [user.userId];
    var query = `SELECT * FROM articles WHERE userId = ? LOCK IN SHARE MODE`;
    db.getConnection(function (err, connection) {
        if (err) {
            // An error. Ensure `callback` gets called with the error argument.
            return callback(err);
        }

        connection.beginTransaction(function (err) {
            if (err) {
                // An error. Ensure `callback` gets called with the error argument.
                return callback(err);
            }

            return connection.query(query, params, function (err, result) {
                if (err) {
                    // An error.
                    // Rollback
                    connection.rollback(function () {
                        // Once the rollback finished, ensure `callback` gets called 
                        // with the error argument.
                        return callback(err);
                    });
                } else {
                  // Query success. Call `callback` with results and `null` for error.
                  //console.log(result);
                  return callback(null, result);
                }
            });
        });
    });
}

There's no point in throwing errors inside the callbacks on the connection methods, since these functions are async. Ensure you pass the error to the callback instead, and stop execution (using the return statement).

One more thing, without knowing the full requirements of this: I'm not sure you need transactions for just fetching data from the database, without modifying it; so you can just do the query() and skip on using any beginTransaction(), rollback() and commit() calls.