Timing issue with mysql query in NodeJS

Question

Timing issue with mysql query in NodeJS

I'm using mysql module in nodejs.

I want to do something like this, but the problem is that the callback of query is async and I can't fill the result array correctly.. How can I do? Thanks!

function fn(callback) {
    client.query(
        'SELECT * FROM imbarcazioni',
        function select(err, ships) {
        if(err) {
            throw err;
        }

        ships.forEach(function(ship) {
            client.query(
                'SELECT * FROM storico_imbarcazioni WHERE id_imbarcazione=' + ship.id,
                function select(err, hist) {
                    ship.history = hist;
                }
            );
        });

        callback(hist);
    });
}

mysql
node.js
asynchronous
timing

Answer 1

As usual, I recommend async for these kinds of things. Here, you could use async.map:

function selectHistory(ship, callback) {
    client.query('SELECT * FROM storico_imbarcazioni WHERE id_imbarcazione = ?', [ship.id], function(err, history) {
        if(err) return callback(err);
        ship.history = history;
        callback(null, ship);
    });
}

client.query('SELECT * FROM imbarcazoni', function(err, ships) {
    async.map(ships, selectHistory, function(err, ships) {
        // ships is an array with each ship along with it's history
    });
});

That said, for your particular example, I would rather use a JOIN and handle it in SQL:

SELECT * FROM imbarcazioni
LEFT JOIN storico_imbarcazoni ON storico_imbarcazoni.id_imbarcazione = imbarcazioni.id