Node loop insert with mySQL and Mongodb - mysql

Question

I have a form with one field that allows user to enter multiple developer id via comma delimited (ab1234,bc5678).
Once the form is submitted I perform the following tasks:
Get the the project
Loop through array of developer IDs to get their full name using mySQL
update the project using MongoDB
I'm new and sure this this is possible, The codes I have below is not working for me. Can someone please let me know if the codes below is even close.
const mongoose = require('mongoose'
const mysql = require('mysql');
// Create mySQL connection
const mySQLdb = mysql.createConnection({
host : 'localhost',
user : 'root',
password : 'root',
database : 'projects'
});
const Project = mongoose.model('project');
router.post('/developerSave', async (req, res) => {
let devList = req.body.dev_ids,
devIdArr = devList.split(','),
rData = {};
// get project
const project = await Project.findById(req.body.projectID);
mySQLdb.connect();
for(var i=0, len=devIdArr.length; i < len; i++) {
let sql = `SELECT CONCAT(first_name, ' ', last_name) as full_name FROM users WHERE id= '${devIdArr[i]}'`;
mySQLdb.query(sql, function (err, results) {
if (err) throw err;
let newDev = {
userId: devIdArr[i],
fullName: results[0].full_name
}
project.developers.unshift(newDev);
await project.save();
});
}
mySQLdb.end();
rData.success = true;
rData.msg = 'Developer was added successfully.';
res.status(200).json(rData);
});

Answer 1

The reason you are seeing this is because your await project.save(); is inside the callback function. Your main function will not wait for all the callbacks to complete and close the db connection. Lets look at the example below
const myCallback = (param, callback) => {
setTimeout(() => {
console.log('callback function', param);
callback();
}, 1000)
}
const myAsync = async () => {
console.log('inside async');
const result = await axios.get('http://google.com/');
for (let i = 0; i < 10; i++) {
myCallback(i, () => {
console.log('this is the actual callback function');
});
}
const result2 = await axios.get('http://bing.com/');
console.log('after second call');
}
myAsync();
The output of this is
inside async
after second call
callback function 0
this is the actual callback function
...
As you can see, the after second call is printed before the callback functions.
To solve this problem, you can wrap your callback function in a promise and resolve that once save is complete.