Node.js mysql error cannot read property of undefined?

Question

I have a program that inserts SMDR data into a database as it comes in.

Here is my code:

var net = require('net'),
    mysql = require('mysql'),
    PORT = 1752,
    HOST = '192.168.10.2',
    pool = mysql.createPool({
        host: 'localhost',
        port: 3307,
        user: 'root',
        password: 'root',
        database: 'mydb'
    });

function connectionListener(conn) {
    console.log('Listening for incoming calls...');
}

function logCall(phonenumber, operator) {
    pool.getConnection(function(err, connection) {
        if (!err) { // If no error exists 
            var opquery = connection.query('SELECT OperatorID FROM tblOperators WHERE Phone_Login = ' + operator, function(err, rows) {
                if (err) {
                    console.error(err);
                    connection.release();
                    return;
                }
                var query = connection.query('INSERT INTO incoming_calls(phone_number, OperatorID) VALUES("' + 
                phonenumber + '", "' + rows[0].OperatorID + '") ON DUPLICATE KEY UPDATE OperatorID=OperatorID, date_created=NOW()', function(err, rows) {
                    if (err) {
                        console.error(err);
                    }
                    connection.release();
                });
            });
        } else {
            console.error(err);
        }
    });
}

function processdata(data) {
    var phonedata = data.toString().match(/([0-9]?)([0-9]{10})/),
        operdata = data.toString().match(/([*])([0-9]{4})/);
    if (phonedata !== null && operdata !== null) {
        var phonenumber = phonedata[2], 
            oper = operdata[2];

        oper = oper.replace('*', '');
        phonenumber = phonenumber.slice(0,3)+"-"+phonenumber.slice(3,6)+"-"+phonenumber.slice(6);
        logCall(phonenumber, oper);
    }
}
logCall('999-999-9999', '1203');
var conn = net.createConnection(PORT, HOST, connectionListener);
conn.on('data', processdata);
conn.setEncoding('utf8');

And here is the error that I get, when OperatorID clearly does exist within the table:

c:\xampp\htdocs>node listener
Listening for incoming calls...

c:\xampp\htdocs\node_modules\mysql\lib\protocol\Parser.js:82
        throw err;
          ^
TypeError: Cannot read property 'OperatorID' of undefined
    at Query._callback (c:\xampp\htdocs\listener.js:27:48)
    at Query.Sequence.end     (c:\xampp\htdocs\node_modules\mysql\lib\protocol\sequences\Sequence.js:96:24)
    at Query._handleFinalResultPacket     (c:\xampp\htdocs\node_modules\mysql\lib\protocol\sequences\Query.js:143:8)
    at Query.EofPacket (c:\xampp\htdocs\node_modules\mysql\lib\protocol\sequences\Query.js:127:8)
    at Protocol._parsePacket (c:\xampp\htdocs\node_modules\mysql\lib\protocol\Protocol.js:271:23)
    at Parser.write (c:\xampp\htdocs\node_modules\mysql\lib\protocol\Parser.js:77:12)
    at Protocol.write (c:\xampp\htdocs\node_modules\mysql\lib\protocol\Protocol.js:39:16)
    at Socket.<anonymous> (c:\xampp\htdocs\node_modules\mysql\lib\Connection.js:82:28)
    at Socket.emit (events.js:95:17)
    at Socket.<anonymous> (_stream_readable.js:764:14)

Does anyone have any ideas as to why this would happen, I have a production database that uses this, has the same exact information and it works?

looks like rows[0] is undefined. If you ever get an empty result set, you're going to run into this problem. A good practice here would be to capture the relevant row in its own variable, and check its existence before trying to access any of its potential values. You could also create a guard clause that just returns if rows.length < 1, preventing any further execution and avoiding this problem. — Jordan Foreman
– Jordan Foreman, Commented Dec 22, 2014 at 22:05
On my production database, I can truncate the whole table 'incoming_calls', and rerun this script, and it will run just fine, but when I try to run on my secondary database, it just doesn't work for some reason. — Juan
– Juan, Commented Dec 22, 2014 at 22:15
tblOperators is loaded with data on both databases, so OperatorID is defined, this cannot be the issue. — Juan
– Juan, Commented Dec 22, 2014 at 22:16
What was it? It might be worth adding your solution as an answer in case anyone else has this same issue — Jordan Foreman
– Jordan Foreman, Commented Dec 23, 2014 at 3:29

Alex · Accepted Answer · 2016-08-29 05:22:32Z

first check your query result is blank or not if it blank than you will get that error ex.

var opquery = connection.query('SELECT OperatorID FROM tblOperators WHERE Phone_Login = ' + operator, function(err, rows) {
            if (err) {
                console.error(err);
                connection.release();
                return;
            }
            else
            {
              if(rows!="")
              {
                  var query = connection.query('INSERT INTO incoming_calls(phone_number, OperatorID) VALUES("' + 
            phonenumber + '", "' + rows[0].OperatorID + '") ON DUPLICATE KEY UPDATE OperatorID=OperatorID, date_created=NOW()', function(err, rows) {
                if (err) {
                    console.error(err);
                }
                connection.release();
            });
              }
              else
              {
                  console.log('can not get data from tabel');
              }
            }

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