Mongoose document created. But change is not reflected immediately in the collection - node.js

Question

favoriteRouter
.route('/:dishId')
.post(cors.corsWithOptions, authenticate.verifyUser, (req, res, next) => {
Favorites.findOne({ user: req.user._id })
.then(
(favoriteList) => {
//***SECTION A START//***
if (favoriteList == null) {
Favorites.create({
user: req.user._id,
})
.then(
(favoriteList) => {
console.log('promise resolved');
},
(err) => {
console.log('promise error');
next(err);
}
)
.catch((err) => next(err));
}
//***SECTION A END//***
Favorites.findOne({ user: req.user._id })
.then((favoriteList) => {
//***SECTION B START//***
if (favoriteList != null) {
favoriteList.dishes.push(req.params.dishId);
favoriteList
.save()
.then(
(favoriteList_c) => {
res.statusCode = 200;
res.setHeader('Content-Type', 'application/json');
res.json(favoriteList_c);
},
(err) => {
next(err);
}
)
.catch((err) => {
next(err);
});
} else {
err = new Error(
'Something wrong with favorite list document of user ' +
req.user._id
);
err.status = 404;
return next(err);
}
//***SECTION B END//***
})
.catch((err) => next(err));
},
(err) => next(err)
)
.catch((err) => next(err));
});
If a user post on /:dishId and the favourite document is not there for that user then a new document is created
in SECTION A (marked in code). The document is created fine as it prints promise resolved. But in SECTION B the else part is executed that means the newly created document is not found. But if the user tries again means in next go it can find that document and it gets updated in SECTION B IF block. Is there something I am missing. I am a beginner in nodejs, Please help!

Answer 1

You have to first understand the way NodeJs asynchronous code work. The default behavior of NodeJs is that whenever it finds an I/O operation, it delegates that opeation to either OS or worker thread based on OS capability in handling it and moves to the next line of code.
According to your code, the first Favorite.findOne() is called and while it is being executed by the engine, control jumps over to the next line of code, which is the second Favorite.findOne() and it tries to find the document. But At this point the document has not been created yet, So that's the reason when you run for the first time, it doesn't find the record, but for the second time onwards the document has been created using the Favorite.create() inside the first findOne's then().
So you need to re-factor your code by putting the second findOne() inside the firstOne. Well, you know what, you don't need to write the Favorite.findOne() two times. One findOne() is sufficient to accomplish your requirement.
Mongoose leverages promises, it means we can use async/await in the controller method.
favoriteRouter
.route('/:dishId')
.post(cors.corsWithOptions, authenticate.verifyUser, async (req, res) => {
try {
// find the FavoriteList
let favoriteList = await Favorites.find({
user: req.user._id
});
// using a library called lodash for simplicity
// you have to install it using npm i lodash and
// require at the top using let _ = require('lodash')
//If not found, create one and assign it to favorite list
if (_.isEmpty(favoriteList)) {
favoriteList = await Favorites.create({
user: req.user._id
});
}
// at this point, you must have a favoriteList either a found one or brand new
favoriteList.dishes.push(req.params.dishId)
let favoriteList_c = await favoriteList.save();
return res.json(favoriteList_c)
} catch (err) {
//handle error
res.status(501).send({message: 'unable to perform operation'});
}
});
I have added async to the controller callback function here and reomved the next parameter, as we don't need it. For reference visit this.
NOTE: the code I've wrtitten may not work if you simply copy/paste it in your program but the approach is fairly straight forward and you may need to do some tweakings based on Mongoose API documentation especailly for save() and create().
I am sure they will return the object after creating it.
Good Luck!!

Answer 2

There is no problem in your code but when the findOne of section A is getting executed at the same time section B code gets executed.
Using promise.then creates a complex code. Use async/await instead.
The following is just a small snippet from your code to use async/await
let favoriteList = await Favorites.findOne({ user: req.user._id });
if (favoriteList == null) {
await Favorites.create({
user: req.user._id,
})
}
favoriteList = await Favorites.findOne({ user: req.user._id })
if (favoriteList != null) {
favoriteList.dishes.push(req.params.dishId);
await favoriteList.save();
res.statusCode = 200;
res.setHeader('Content-Type', 'application/json');
res.json(favoriteList_c);
} else {
err = new Error(
'Something wrong with favorite list document of user ' +
req.user._id
);
}