handling mysql connection with nodejs

Question

I'm trying to set-up a function for connecting to MySQL so other functions can call it and get a connection in return. Here is my code based on documentation:

function connect_to_mysql(){
    var con = mysql.createConnection({
        host: "localhost",
        user: "roots",
        password: "",
        database: "mydb"
    });



    con.connect(function(err) {
        if (err)
        {
            throw err;
        }

    });

    return con ;

}

function do_stuff () {
    connection = connect_to_mysql();
    console.log('--------------------------------------------------');
    console.log('ALL OK ## ');
    return ;
}

Here is the problem: let's say there is a error on connection. I get this output in terminal:

--------------------------------------------------
ALL OK ##
D:\wamp\www\pop\node_modules\mysql\lib\protocol\Parser.js:80
        throw err; // Rethrow non-MySQL errors
        ^

Basically the code goes on and I get ALL OK ## before throw err

I want to abort the code if connection fails .... to put it very simply I want connect_to_mysql to return false if connection fails so I can abort the process.

are you using the account called roots or are you trying to use the root account? — mathmaniac88
– mathmaniac88, Commented Aug 8, 2018 at 18:13
@awesomeguy its root account im trying to generate error so i put roots instead of root — hretic
– hretic, Commented Aug 8, 2018 at 18:15

Martín Zaragoza · Accepted Answer · 2018-08-08 18:21:43Z

The problem here is that the connect function is async, that's why it receives a callback:

con.connect(function(err) {
    if (err)
    {
        throw err;
    }
});

When you run do_stuff, console.log('--------------------------------------------------'); console.log('ALL OK ## '); and function(err) { if (err) { throw err; } } run at the same time.

I'd suggest changing your connect_to_mysql function to receive a callback that will be called after establishing a connection:

function connect_to_mysql( callback ){
    var con = mysql.createConnection({
        host: "localhost",
        user: "roots",
        password: "",
        database: "mydb"
    });

    con.connect(function(err) {
        if (err){
            throw err;
        } else {
            callback(con);
        }

    });
}

Then you can do something like:

connect_to_mysql( conn => {
    console.log("all ok");
    // run queries ...
});

Your callback function could also handle errors in case the connection fails:

function connect_to_mysql( callback ){
    var con = mysql.createConnection({
        host: "localhost",
        user: "roots",
        password: "",
        database: "mydb"
    });

    con.connect(callback);
}


connect_to_mysql( function(err,conn) {
    if(err) { //abort };

    console.log("all ok");
    // run queries ...
});

Hope this helps

mathmaniac88 · Accepted Answer · 2018-08-08 18:22:49Z

0

If you want to actually display the error you should do console.log(err);

I think the main use of throw err; is to stop the script since I ran a test with console.log(err) but not throw err; and it displayed the error but the program kept running.

answered Aug 8, 2018 at 18:22

mathmaniac88

6408 silver badges23 bronze badges

Comments

Sookie Singh · Accepted Answer · 2018-08-08 18:23:31Z

0

You can do something like this:

function connect_to_mysql(callback) {
    var con = mysql.createConnection({
        host: "localhost",
        user: "roots",
        password: "",
        database: "mydb"
    });
    con.connect(function(err) {
        if (err) {
            callback(err);
        } else {
            callback(null, con);
        }
    });
}

function do_stuff() {
    connect_to_mysql(function(err, connection) {
        if (err) {
            //abort
        } else {
            console.log('--------------------------------------------------');
            console.log('ALL OK ## ');
            return;
        }
    });
}

answered Aug 8, 2018 at 18:23

Sookie Singh

1,62313 silver badges17 bronze badges

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