How to get asynchronous data using nodejs

Question

I am attempting to get data from a mysql table using nodejs. I call the sql routine which is in another node js file. However, I cannot get my callback to return the data. I think the problem might be that I am calling an asynchronous routine from a node js file rather than from an angular or regular javascript program. Below is the exports script I am calling.

exports.getVenueById = function(db, id) {
    var http = require('http');
    var mysql = require('mysql');

    var query = "SELECT *  FROM venues WHERE auto_increment = ? "
    query = mysql.format(query, id);
    console.log("query=" + query);

db.query(
    query,
    function(err, rows) {
        if(err) console.log("error=" + err);
        console.log("rows=" + rows[0]['auto_increment']);
        res.json({success: true, response: rows});
        //return rows[0];
     });

}

I know this is working because I am writing the results to the console. The problem is the data never gets back to the calling node js routine below.

function getVenueData (id , callback)  {             
  (function () {
     venueData = venueTable.getVenueById(db, id);           
     if(venueData) {
         callback();
         console.log("callback in loop");
      }
      console.log("callback after loop");        
  });        
}

getVenueData(id, gotVenueData);

The program immediately returns and displays the timeout message. I admit that I am not an expert in nodejs or its callback feature. I would appreciate any feedback as to how I can get the program to wait for the asynchronous data to return to the calling program.

function gotVenueData() {
  console.log("gotVenueData");
}

setTimeout(function() { console.log("timeout for 10 seconds");} , 10000);
console.log("venuedata=" + venueData);

It's not considered as answer, but there's a typo in your first code part. You're missing a semicolon behind var query = "SELECT * FROM venues WHERE auto_increment = ? " It's also missing in the answer of @SomeKittens — morten.c
– morten.c, Commented Mar 27, 2014 at 1:34
@morten.c odd, didn't get pinged there. Fixing it in my answer. It's not too serious of a typo, as JS will automatically add it. — SomeKittens
– SomeKittens, Commented Mar 27, 2014 at 1:38

SomeKittens · Accepted Answer · 2014-03-27 01:38:45Z

5

You're trying to return async data syncronously. Instead, add a callback to getVenueById:

exports.getVenueById = function (db, id, cb) { var http = require('http'); var mysql = require('mysql');

var query = "SELECT *  FROM venues WHERE auto_increment = ? ";
query = mysql.format(query, id);
console.log("query=" + query);

db.query(
query,

function (err, rows) {
    if (err) console.log("error=" + err);
    console.log("rows=" + rows[0]['auto_increment']);
    cb({
        success: true,
        response: rows
    });
    //  return rows[0];
});

and use it as such:

venueTable.getVenueById(db, id, function(data) {
  console.log(data);
});

One caveat: Traditionally the callback has the first parameter as the error (or null) and then the actual data. With that in mind:

exports.getVenueById = function (db, id, cb) { var http = require('http'); var mysql = require('mysql');

var query = "SELECT *  FROM venues WHERE auto_increment = ? ";
query = mysql.format(query, id);
console.log("query=" + query);

db.query(
query,

function (err, rows) {
    if (err) { cb(err); }
    console.log("rows=" + rows[0]['auto_increment']);
    cb(null, {
        success: true,
        response: rows
    });
    //  return rows[0];
});

and use it as such:

venueTable.getVenueById(db, id, function(err, data) {
  if (err) { return console.log(err); }
  console.log(data);
});

edited Mar 27, 2014 at 1:38

answered Mar 27, 2014 at 1:25

SomeKittens

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2 Comments

Dave Over a year ago

Wow! Thanks for educating me in the world of callbacks. I applied your changes and data is coming back. I need to brush up more on callbacks as that is the power of nodejs. I scoured the internet trying to find an example of what I wanted to do and you are the one who showed me. Thanks a million!

frankish Over a year ago

How do you get the correct last_insert_id with an async mysql insert query?

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