mongoose save by reference multiple document - express

Question

I'd like to make new document by reference of two documents.
**app.post('/student_badge/register', async (req, res) => {
const name = req.body.name;
const category = req.body.category;
People.find({name: name}, '_id', function (err, doc) {
if (err) return handleError(err);
var obj = eval(doc);
id = obj[0]._id;
})
Badge.find({category: category}, 'points title', function (err, doc) {
if (err) return handleError(err);
var obj2 = eval(doc);
points = obj2[0].points;
title = obj2[0].title;
console.log(title + " " + points);
});
data = {
id: id,
title: title,
points: points
}
console.log("data: " + data);
const sbadge = new StudentBadge(data);
sbadge.
save()
.then(result => {
res.status(201).json({
message: 'Post created successfully!',
post: result
});
})
.catch(err => {
console.log(err);
});
});**
But I cannot call three variables like id, title, points to store them in 'data'.
How can I call variables?
Thanks

Answer 1

Your code does not work because the variables you are trying to access, i.e. id, title, points, are being set on a callback function that gets executed asynchronously.
I would suggest using async/await instead of callbacks so that you can thereafter use the data from the other documents you are querying in the same function. In addition, I suggest to use findOne() since you only access the first entry in db.
Something like the example below should work: (I have abstracted the middleware in a separate function for clarity to use with express)
const createStudentBadge = async (req, res, next) => {
const {name, category} = req.body;
let person, badge;
try {
person = await Person.findOne({name}); // shortcut for {name: name}
badge = await Badge.findOne({category});
} catch(err) {
// handle error
}
if (!person || !badge) {
// Handle case where no document has been found in db
// This case will not throw an error when calling find()
}
data = {
id: person._id,
title: badge.title,
points: badge.points
}
const studentBadge = new StudentBadge(data);
try {
await studentBadge.save();
} catch(err) {
// handle error
}
res.status(201).json({
message: 'Post created successfully!',
post: studentBadge
});
}
app.post('/student_badge/register', createStudentBadge);
If you wanted to perform the querying in parallel, you could make use of Promise.all() and run both queries at the same time. More info can be found at MDN documentation