How to detect/specify when no mysql data is returned from a nodejs query

Question

I am trying to detect when nodejs receives no data back from a mysql query. If the data that is put through a GET request is correct, it gives back the desired results.

Working Request:

http://server.com:8000?a=userinfo&user=datathatmatchesvalueindb

Non-Working Request

http://server.com:8000?a=userinfo&user=datathatdoesn'tmatchanythinginthedb

By non-working, I mean if the request includes data that is not in the mysql table, it displays a blank white page, instead of the desired result of 'no data'.

In PHP if you want to detect if there is no data in the mysql row, you can do the following:

if($res->num_rows === 0)
{
    echo 'no data';
} else {
//Do you functions here
}

Is there an equivalent for nodejs code?

Here is the code I have written:

var express = require('express');
var app = express();
var database = require('mysql-simple');

app.get('/', function(req, res){

database.init('user', 'pass', 'db', 'IP');
var data = '';
if (req.query.a == 'userinfo') {
var q = 'SELECT * FROM `addrbook` WHERE `key` =\''+req.query.user+'\'';
} else if (req.query.a == 'facebook') {
var q = 'SELECT * FROM `addrbook` WHERE `facebook` =\''+req.query.fb+'\' OR `facebookp` =\''+req.query.fb+'\'';
} else if (req.query.a == 'youtubeurl') {
var q = 'SELECT * FROM `addrbook` WHERE `youtubeurl1` =\''+req.query.url+'\' OR     `youtubeurl2` =\''+req.query.url+'\' OR `youtubeurl3` =\''+req.query.url+'\'';
} else {
var q = 'SELECT * FROM `addrbook` WHERE `key` =\''+req.query.user+'\'';
}
database.query(q, function(err, rows, fields)
{
   if (err) {
    console.log('error fetching user data: ' + err);
    return;
  }
    //console.log(results);
   for (var i = 0; i < rows.length; i++) {
    var row = rows[i];
    if(rows.length > 0) {
        var key = row['key'];
        var fb = row['facebook'];
        var daddr = row['addr'];
        if (req.query.a == 'userinfo') {

        data = JSON.stringify(row);
        res.write(data);

        } else if (req.query.a == 'facebook') {

        data = JSON.stringify(daddr);
        res.write(data);

        } else if (req.query.a == 'youtubeurl') {

        data = JSON.stringify(daddr);
        res.write(data);

        } else {
        res.write('no data');
        }
    } else {
        res.write('no data');
        console.log('no data');
    }
   }
    res.end();
});

});
app.listen(8000);

check to be sure you are using res.send() to get data out, and call next() to keep the response chain going. — clay
– clay, Commented Feb 28, 2014 at 19:49
Take a look in the expressjs API and seach for "next()". It's really a middleware thing to keep response flow going. You may not need it (at least for now). — clay
– clay, Commented Feb 28, 2014 at 20:03
So far I don't believe I need it, though I will try and implement it. Do you have any idea why it won't display 'no data' when the mysql query returns no nothing for no data in existing in a row? — user3259138
– user3259138, Commented Feb 28, 2014 at 20:17

gnerkus · Accepted Answer · 2016-01-19 07:27:02Z

1

Because your res.write("no data") is inside loop for...rows and as there are no rows it is never called.

edited Jan 19, 2016 at 7:27

gnerkus

12.2k7 gold badges54 silver badges76 bronze badges

answered Jan 19, 2016 at 6:59

iw2rmb

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