Node.js & MySQL: HTTP server stops after first run

Question

I'm using node-mysql. Below codes taken from http://blog.josedacruz.com/2013/07/19/learning-node-js-using-mysql/

var http = require('http');
var mysql = require('mysql');

var connection = mysql.createConnection({
  host : 'localhost',
  port : 3306,
  database: 'aaa',
  user : 'root',
  password : 'z'
});

http.createServer(function(req, res){
    res.writeHeader(200);
    res.write('Connect to mySql\n');
    // Connect to mySql (if there is an erro, report it and terminate de request)
    connection.connect(function(err){
        if(err != null) {
            res.end('Error connecting to mysql:' + err+'\n');
        }
    });

    connection.query("SELECT value FROM variable WHERE name = 'site_name'", function(err, rows){
        if(err != null) {
            res.end("Query error:" + err);
        } else {
            // Shows the result on console window
            console.log(rows[0]);
            res.end("Success!");
        }
        // Close connection
        connection.end();
    });
}).listen(80);

First thing first, I feel strange the connection.end not same level with connection.connect

I've tried change the connection to be same level and also put on different place, but still no luck

Below is the error in terminal when HTTP server stops after first run (note: MyTube is the result of query)

{ value: 'MyTube' }
 
Error: Cannot enqueue Quit after invoking quit.
    at Protocol._validateEnqueue (/home/mydir/node/node_modules/mysql/lib/protocol/Protocol.js:131:16)
    at Protocol._enqueue (/home/mydir/node/node_modules/mysql/lib/protocol/Protocol.js:98:13)
    at Protocol.quit (/home/mydir/node/node_modules/mysql/lib/protocol/Protocol.js:61:36)
    at Connection.end (/home/mydir/node/node_modules/mysql/lib/Connection.js:155:18)
    at Query._callback (/home/mydir/node/app.js:31:20)
    at Query.Sequence.end (/home/mydir/node/node_modules/mysql/lib/protocol/sequences/Sequence.js:75:24)
    at Protocol._validateEnqueue (/home/mydir/node/node_modules/mysql/lib/protocol/Protocol.js:153:6)
    at Protocol._enqueue (/home/mydir/node/node_modules/mysql/lib/protocol/Protocol.js:98:13)
    at Connection.query (/home/mydir/node/node_modules/mysql/lib/Connection.js:140:25)
    at Server.<anonymous> (/home/mydir/node/app.js:22:16)
    --------------------
    at Quit.Sequence (/home/mydir/node/node_modules/mysql/lib/protocol/sequences/Sequence.js:15:20)
    at new Quit (/home/mydir/node/node_modules/mysql/lib/protocol/sequences/Quit.js:8:12)
    at Protocol.quit (/home/mydir/node/node_modules/mysql/lib/protocol/Protocol.js:61:45)
    at Connection.end (/home/mydir/node/node_modules/mysql/lib/Connection.js:155:18)
    at Query._callback (/home/mydir/node/app.js:31:20)
    at Query.Sequence.end (/home/mydir/node/node_modules/mysql/lib/protocol/sequences/Sequence.js:75:24)
    at Protocol._validateEnqueue (/home/mydir/node/node_modules/mysql/lib/protocol/Protocol.js:153:6)
    at Protocol._enqueue (/home/mydir/node/node_modules/mysql/lib/protocol/Protocol.js:98:13)
    at Connection.query (/home/mydir/node/node_modules/mysql/lib/Connection.js:140:25)
    at Server.<anonymous> (/home/mydir/node/app.js:22:16)

robertklep · Accepted Answer · 2014-01-01 09:39:56Z

2

The problem is that you're trying to reuse a connection created by mysql.createConnection after that connection has been closed by connection.end().

You need to move the call to mysql.createConnection to inside the callback to http.createServer, or (which I would recommend) use connection pooling instead.

answered Jan 1, 2014 at 9:39

robertklep

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Comments

Madhur · Accepted Answer · 2014-01-01 09:45:22Z

1

One way to quickly solve this is to remove your connection.connect and connection.end calls and rely on the implicit connection made by connection.query

http.createServer(function(req, res){
    res.writeHeader(200);
    res.write('Connect to mySql\n');     
    connection.query("SELECT value FROM variable WHERE name = 'site_name'", function(err, rows){
        if(err != null) {
            res.end("Query error:" + err);
        } else {
            // Shows the result on console window
            console.log(rows[0]);
            res.end("Success!");
        }
    });
}).listen(80);

edited Jan 1, 2014 at 9:45

answered Jan 1, 2014 at 9:40

Madhur

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1 Comment

robertklep Over a year ago

node-mysql queues operations so they don't have to be performed in the usual async way of waiting until a previous operation has finished. See the introduction.

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