Get data from findOne mongoose inside another findOne function - node.js

Question

I am trying to get the candidate or HR (user roles) object using mongoose and nodejs. I have a user and both roles are derived from it.
when trying to connect using a UNIQUE username and a password. A user object will be sent as a result. I want to also send candidate/ or HR that are linked to that user.
I am passing the user object by reference to the candidate/HR schema:
const candidateSchema = new Schema({
user: {
type: mongoose.Schema.Types.ObjectId,
ref: "User",
index: true,
},
fullName: String,
profilePhoto: String,
birthday: Date,
I need to get the candidate object of the user that i get inside the exec() function. save it in a variable and send it as a res to signin function
app.post("/api/auth/signin", (req, res) => {
User.findOne({
username: req.body.username,
})
.populate("roles", "-__v")
.exec((err, user) => {
if (err) {
res.status(500).send({ message: err });
return;
}
const candi = candidat.findOne({ user: user }).exec((err, candidate) => {
//I want to save the candidate var
}));
//console.log("res",candi);
.....
});

Answer 1

A simple solution will be to wrap your code inside a promise and resolve whatever you want to store to variable while reject when you want to send error.
But its recommended to break down your code to multiple async functions and await them instead of using callback exec functions.
app.post("/api/auth/signin", async (req, res) => {
try{
let response = await new Promise((resolve,reject)=>{
User.findOne({
username: req.body.username,
})
.populate("roles", "-__v")
.exec((err, user) => {
if (err) {
//REJECT ERROR
reject(err);
return;
}
const candi = candidat.findOne({ user: user }).exec((err, candidate) => {
//RESOLVE YOUR CANDIDATE
resolve(canditate);
}));
//console.log("res",candi);
.....
});
.... your rest of code
})
res.send(response) // or required json
}catch(err){
res.status(500).send({ message: err });
}
}