CODEWITHSUNDEEP
javascriptnode.jsmongodbmongoosesynchronous
Ertan D.
Ertan D.

Reputation: 832

How to synchronise multiple RESTFul requests when using NodeJS and saving to MongoDB?

I have been trying to implement a RESTFul API with NodeJS and I use Mongoose (MongoDB) as the database backend.

The following example code registers multiple users with the same username when requests are sent at the same time, which is not what I desire. Although I tried to add a check!

I know this happens because of the asynchronous nature of NodeJS, but I could not find a method to do this properly. It looks like "findOne" method immediately returns, causing registerUser to return and then another request is processed.

By the way, I don't want to check for existing users with a separate API function, I need to check at the registration stage. Is there any way to do this?

Controller.prototype.registerUser = function (req, res) {
    Users.findOne({'user_name': req.body.user_name}, function(err, user) {
        if(!user) {
            new User({user_name: req.body.user_name}).save(function(err) {
                if(!err) {
                    res.send("User saved");
                } else {
                    res.send("DB Error: Could not save user!");
                }
            });
        } else {
            res.send("User exists");
        }
    });
}

Upvotes: 1

Views: 227

Answers (2)

patalmypal
patalmypal

Reputation: 6712

You should consider setting the user_name to be unique in the Schema. That would ensure that the user_name stays unique even if simultaneous requests are made to set an identical user name.

Upvotes: 2

BFree
BFree

Reputation: 103770

Yes, the reason this is happening is as you suspected because multiple requests can execute the code simultaneously and therefore the User.fineOne can return false multiple times. Incidentally this can happen with other stacks as well, even ones that use one thread per request.

To solve this, you need a way to somehow either control that just one user is being worked on at the time, you can accomplish this by adding all registerUser requests to a queue and then pulling them off the queue one by one and calling res.Send only after it's processed form the queue.

Alternatively, maybe you can keep a local array of user names, and each time a new request comes in and check the array if it's already there. If it isn't add it to the array and work on it. If it is in the array, send the response "User exists". Then, once the user has been successfully created, you can remove it from that array. (I haven't thought this one through 100% but I think it should work as well.)

Upvotes: 1

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