Cannot enqueue Handshake after invoking quit

I have implemented the following code:

module.exports = {
    getDataFromUserGps: function(callback)
    {
        connection.connect();
        connection.query("SELECT * FROM usergps", 
            function(err, results, fields) {
                if (err) return callback(err, null);
                return callback(null, results);
            }
        ); 
        connection.end();
    },
    loginUser: function(login, pass, callback)
    {
        connection.connect();
        connection.query(
            "SELECT id FROM users WHERE login = ? AND pass = ?",
            [login, pass],
            function(err, results, fields) 
            {
                if (err) return callback(err, null);
                return callback(null, results);
            }
        ); 
        connection.end();
    },
    getUserDetails: function(userid, callback)
    {
        connection.connect();
        connection.query(
            "SELECT * FROM userProfilDetails LEFT JOIN tags ON userProfilDetails.userId = tags.userId WHERE userProfilDetails.userid = ?",
            [userid],
            function(err, results, fields)
            {
                if (err) return callback(err, null);
                return callback(null, results);
            }
        );
        connection.end();
    },
    addTags: function(userId, tags)
    {
        connection.connect();
        connection.query(
            "INSERT INTO tag (userId, tag) VALUES (?, ?)",
            [userId, tags],
            function(err, results, fields)
            {
                if (err) throw err;
            }
        )
        connection.end();
    }
}

Everything works great only for the first time. If I want to "use" the query for the second time I get the following error:

Cannot enqueue Handshake after invoking quit

I have tried not to .end() connections but it didn't help.

H