Database access for concurrent API requests

Question

How can one ensure that the database calls are asynchronous for concurrent API calls?

For example, I have this model that represents a pool.

{
    limit: number e.g 5
    isOpen: boolean // will close when users.length == limit
    users: []
}

I want that at any given time, there's only 1 non-full pool in the DB. So I have something like this that runs on an API call.

let openPool = model.findOne({isOpen: true});
if(!openPool){

    //create a new pool
    model.insert({
        limit: 5,
        users: [currentuser]
        isFull: false
    });
}else{

    //add the current user to existing open pool
    model.update({
        users: {$push: {currentuser}}
    });

    //close pool if full
    if(model.users.length == model.users.limit){
        model.update({
            isOpen: {$set: false}
        });
    }

}

When I send 10 requests at the same time to this endpoint, each of them thinks they are the 1st and then create a new pool. So I end up with new 10 pools where I expected 2 full (closed) pools of 5 users each.

Is there a way to ensure that all these requests execute sequentially?

Maybe sequentially is a bad idea. But overall, I'm looking for a way to keep the state of the DB always be valid.

Is Nodejs good for this?

Any pointers to the right direction will be much appreciated.

Answer 1

The solution was to use a mutex to synchronize the critical block.
I used async-lock

var AsyncLock = require('async-lock');
var lock = new AsyncLock();

requestHandler(){
    return new Promise(async (resolve,reject) => {
        lock.acquire('key', async () => {
           let openPool = await model.findOne({isOpen: true});
           if(!openPool){

           //create a new pool
           await model.insert({
               limit: 5,
               users: [currentuser]
               isFull: false
           });
        }else{
            //add the current user to existing open pool
            await model.update({
                users: {$push: {currentuser}}
            });

            //close pool if full
            if(model.users.length == model.users.limit){
                model.update({
                    isOpen: {$set: false}
                });
            }
        }

        return resolve(true);
    }).then(() => {
        //lock released
    });
}