MongoDB.find() 和 MongoDB.findone() 每次都返回 null？

Question

I have a nodejs server connected to a MongoAtlas db. The nodejs server inserts data just fine into the collection, but whenever I attempt to find data it always ends up returning null. I have one document in a "Users" collection in my test cluster. but even when I query for everything my results(res) turn up null.

function isUsernameTaken(userData)
{
    connection.then(() =>{
        const db = client.db("test");
        console.log(db.collection('Users').find({}));

        db.collection('Users').find({username:userData.username}, function(err,res){
            
            console.log(res.length);

            if(err)
            {
                throw err;
            }

            if(res[0])
            {
                return true;
            }else
            {
                return false;
            }
        });
    })
}

This code is one of my functions that involve db.collection.find , but for all the other functions I have essentially the same query and no luck. Something else I tried were to query the exact document from inside the collection( id , username , password ) but once again no luck.

EDIT: res is not null or undefined, res just does not return any documents from my db.

Answer 1

IMO, the async/await syntax is so much easier to write, read, and deal with than the good old Promise and callback hell:

async function isUsernameTaken(userData)
{
    try{
        const res = await db.collection('Users').findOne({ username: userData.username });
        console.log(res);
        return !!res; // Casts truthy/falsy value to boolean. This does in fact return a value from isUsernameTaken().
    } catch(err) {
        throw err;
    }
}

And then you use it this way:

const isItTaken = await isUsernameTaken(someUserDataHere);