i am getting cannot read property 'query' of undefined - node.js

Question

i have make a socket.io chatroom and i am using some database queries to insert and select data but unfortunately i am getting some error of query
The code of the file on which i am getting error is as follow
var rooms = [];
module.exports.getUserFeeds = function (chatpage, socket, io, pool,async)
{
socket.on('senddata', function (data)
{
socket.user_id = data.user_id;
socket.room_id=data.room_id;
socket.room = 'room' + data.room_id;
rooms['room' + data.room_id] = 'room' + data.room_id;
socket.join('room' + data.room_id);
pool.getConnection(function (err, connection)
{
async.parallel([
function(callback)
{
connection.query('SELECT user_id,username FROM chat_users where user_id=' + data.user_id + '', function (error1, userdata)
{
if (error1) return callback(error1);
callback(null, userdata);
});
},
function (callback)
{
if(data.user_id)
connection.query('SELECT user_id,username FROM chat_users', function (error3, memdata)
{
if (error3) return callback(error3);
callback(null, memdata);
});
else
callback(null,null);
},
function(callback)
{
if(data.user_id)
connection.query('SELECT comment_id,comment,chat_users.user_id,username,comments.added FROM comments INNER JOIN chat_users ON comments.user_id=chat_users.user_id',function(error4,converdata){
if (error4) return callback(error4);
callback(null, converdata);
});
else
callback(null,null);
}
], function (err, results)
{
if(err) throw err;
socket.emit('chatdata',
{
memdata:results[1],
converdata:results[2],
});
socket.broadcast.to('room'+ data.room_id +'').emit('newuser', {userdata:results[0]});
connection.release();
});
});
});
socket.on('sendcomment', function (data)
{
pool.getConnection(function (err, connection)
{
connection.query('INSERT INTO comments (user_id,comment,added) VALUES (' + data.user_id + ',"' + data.msg + '","' + data.datetime + '")', function (err, result)
{
if (err) throw err;
async.parallel([
function (callback)
{
connection.query('SELECT comments.*,username,comments.added from comments JOIN chat_users ON comments.user_id=chat_users.user_id WHERE comments.comment_id=' + result.insertId + '', function (err2, comments)
{
if (err2) return callback(err2);
callback(null, comments);
});
},
function (callback)
{
connection.query('SELECT count(comment_id) as tot_comment from comments', function (err3, comment_count)
{
if (err3) return callback(err3);
callback(null, comment_count);
});
},
], function (err, results)
{
if (err) throw err;
if (results[0])
{
chatpage. in('room'+ data.room_id +'').emit('showcomment',
{
room_comment: results[0],
comment_count: results[1]
});
}
connection.release();
});
});
});
});
socket.on('disconnect', function ()
{
console.log("user disconnected");
pool.getConnection(function (err, connection)
{
connection.query('DELETE from chat_users where user_id='+socket.user_id+'', function (err, removeuser)
{
if (err) throw err;
});
connection.query('DELETE from comments where user_id='+socket.user_id+'', function (err, removecomments)
{
if (err) throw err;
});
connection.release();
});
socket.broadcast.to('room'+ socket.room_id +'').emit('removeuser', {user_id:socket.user_id});
socket.leave(socket.room);
});
};
and the error i am getting because of this code is
The image of the error i am getting
please can anyone help me regarding this issue
Thanks a lot
Regards

Answer 1

It seems there is error in your mysql connection.try make proper connection first
Step 1: Create the pool (only do this once)
var mysql = require('mysql');
var pool = mysql.createPool({
host : 'hostname',
user : 'username',
password : 'password',
database : 'db_name',
connectionLimit : 10, // this is the max number of connections before your pool starts waiting for a release
multipleStatements : true // I like this because it helps prevent nested sql statements, it can be buggy though, so be careful
});
Step 2: Get a connection
pool.getConnection(function (err, conn) {
if (err)
return res.send(400);
// if you got a connection...
conn.query('SELECT * FROM table WHERE id=? AND name=?', [id, name], function(err, rows) {
if(err) {
conn.release();
return res.send(400, 'Couldnt get a connection');
}
// for simplicity, just send the rows
res.send(rows);
// CLOSE THE CONNECTION
conn.release();
}
});
check this for more detail https://youtu.be/2CeAnrCsBQo
http://fearby.com/article/how-to-setup-pooled-mysql-connections-in-node-js-that-dont-disconnect/

Answer 2

Adding the following 2 parameters solved my problem
queueLimit
connectionLimit
exports.pool = mysqlCon.createPool({
host: host,
user: user,
port: 3306,
password: pass,
database: db,
queueLimit : 0, // unlimited queueing
connectionLimit : 0 // unlimited connections
});
Note : Be careful, this might break your database.

Answer 3

mysql> ALTER USER 'root'#'localhost' IDENTIFIED WITH mysql_native_password BY '< MySQL password >';
mysql> FLUSH PRIVILEGES;

Answer 4

Solved mine by using mysql2 instead of mysql

Answer 5

I also faced this error. It was due to the fact that the server where I hosted MySQL was down and the connection wasn't establishing while I was querying the database. As soon as I started the server again then it all got set.

Answer 6

You need to handle errors, otherwise you can encounter issues like this. Specifically in this case, you aren't checking if err is set in your pool.getConnection() callback. It is most likely set and is why you don't have a valid connection object.