NodeJS and MySQL: getting array data inside query callback - mysql

Question

I'm trying to run this piece of code:
setInterval(function () {
var params = {
QueueUrl: 'https://sqs.us-east-1.amazonaws.com/821808622769/Teste', // required
MaxNumberOfMessages: 10
};
sqs.receiveMessage(params, function (err, data) {
if (err)
console.log('Erro de SQS:' + err);
else {
var retorno = data.Messages;
for (var i in data.Messages) {
var queryString = 'SELECT now()'; //dummy query, just for tests
db_connection.query(queryString, null, function (err, rows, fields) {
if (err) {
console.log('Erro no BD:' + err);
return;
}
var date = new Date();
console.log(retorno[i].Body + ' ' + date.getTime().toString());
});
}
console.log();
}
});
}, 30000);
and I have 5 messages in AWS SQS, such as this:
but when I run my code, instead of having the retorno[i].Body of each message, sometimes I get a message repeated, as show in this image
My for loop is running from 1 to 5 queries, but how do I carry the retorno[i] inside the callback to the database query? I mean, how do I identify which message I was dealing with?

Answer 1

Using .bind() you can setting the internal version of i to be the same as the version of i in your loop.
.bind({i:i}) at the end of your callback and change the internal code to reference this.i
for (var i in data.Messages) {
var queryString = 'SELECT now()'; //dummy query, just for tests
db_connection.query(queryString, null, function(err, rows, fields) {
if (err) {
console.log('Erro no BD:' + err);
return;
}
var date = new Date();
console.log(retorno[this.i].Body + ' ' + date.getTime().toString());
}.bind({
i: i
});
}
}