NodeJS - How does connection.rollback() work with async.parallel - node.js

Question

I'm totally new to nodejs. I would like to ask your expertise regarding for error handling using connection.beginTransaction(); with this sample code.
connection.beginTransaction(function(){
async.parallel([
function(callback){
connection.query('INSERT INTO SUBJECT.PROJECT (Name, Score) VALUES (?,?)',
['Drake', '85']
, function(error){
//if(error)
// connection.rollback();
callback(error);
});
},
function(callback){
connection.query(someUpdateQuery, someValues,
function(error){
//if(error)
// connection.rollback();
callback(error);
});
}
], function(error){
var msg;
if(error) {
connection.rollback();
msg = 'Error! ' + error;
}
else {
connection.commit();
msg = 'Success';
}
res.json(msg);
});
});
With this sample code, Is this doable?
Every connection.query has connection.rollback() in if(error), can I remove connection.rollback() in each
connection.query and rely in the last function instead to handle the
connection.rollback()? - will it rollback all (lets say) 10 inserting query functions then the 5th 1 got the error.
Sorry, I don't know much,. thanks for reading

Answer 1

You are correct - you can remove the rollback statements of the individual queries and rely on the one in the async.parallel callback. Your code would look something like this:
connection.beginTransaction(function () {
async.parallel([
function (callback) {
connection.query('INSERT INTO SUBJECT.PROJECT (Name, Score) VALUES (?,?)',
['Drake', '85']
, callback);
},
function (callback) {
connection.query(someUpdateQuery, someValues, callback);
}
], function (error) {
var msg;
if (error) {
connection.rollback();
msg = 'Error! ' + error;
}
else {
connection.commit();
msg = 'Success';
}
res.json(msg);
});
});
This works because non of the commands will be committed to the database until you call connection.commit() in the final callback. One thing you might want to look at is whether the commit and rollback methods are asynchronous, i.e. they expect you to pass a callback to them. If so your code as it is will run res.json before the transaction has been committed or rolled back.