Integrate mysql in waterfall async - mysql

Question

I need to save to db inside an async waterfall series.
I've tried to integrate these two function after the clean function
function connectDb(next) {
pool.getConnection(function(err, connection) {
if (err) console.log(err);
conn = connection;
}, next);
},
function saveDb(next) {
let sql = "UPDATE media SET media_url = ? WHERE media_url = ?";
conn.query(sql, [dstKey, srcKey], function (error, results, fields) {
if (error) {
conn.release();
console.log(error);
}else{
console.log("media db updated");
}
}, next)
}
The problem is that these two functions block the code execution. How can I integrate it in the function below? I've tried to wrap the function in promise but it is also not working.
async.waterfall([
function download(next) {
s3.getObject({
//param
},
next);
},
function transform(response, next) {
resizeMedia(response.Body ).then( ( file ) => { next();} ).catch( (err) => { reject(err) } ); }
},
function upload(next) {
var fileData = fs.createReadStream('/tmp/'+dstKey);
if (isVideo ) { var ContentType = 'video/mp4' }
if (isAudio ) { var ContentType = 'audio/mp3' }
s3.putObject({
//param
},
next);
},
function clean(next) {
// Stream the transformed image to a different S3 bucket.
fs.unlinkSync('/tmp/'+dstKey);
s3.deleteObject({
//param
},
next);
}
], function (err) {
if (err) {
console.error('Error');
callback(null, "Error");
return;
} else {
console.log('Success');
callback(null, "Done");
return;
}
callback(null, "Done");
return;
}
);

Answer 1

The purpose of async waterflow is to block the waterfall until the callback is called.
P.S. Usually you should not create a new db connection each time. The connection should be done once when the application start and get used whenever you need.
I highly recommend you to use knex.js instead, it return promises by default and if you like to use it inside async waterfall (and wait for resolve) you can call .asCallback.

Answer 2

I've found the problem, if someone fall into the same issue here my solution:
If a waterfall function has a response, this response is automatically added as first argument in the next function. In my code the mistake was simple (after night's sleep), the s3.deleteObject and s3.putObject has response, this response need to be setted as first argument and the callback as last, as you say I've used only the callback as argument (next) and this broke my code.
[...]
function upload(next) {
s3.putObject({
//param
},
next);
},
function clean(response, next) { // response in arguments
s3.deleteObject({
//param
},
next);
}
[...]