Console loggin a MongoDB collection. Undefined

Question

I'm creating a Node project cause i want to knwo how to use mongoose but i'm facing a problem right now. I'm getting an undefined variable while returing a collection from my MongoDB database. This is my code:

app.js

...
case 'index-user':
        let indexUserResponse = userController.index();
        console.log(indexUserResponse); // undefined
        break;
...

user.js (controller)

...
const index = () => {
    User.find({}, function(err, res) {
        if (err) throw err;
        return res;
    });
}
...

I know that there is a user on the database and i can see it if add a console.log(user) just before the return res; so... What is happening here? I don't get it.

Might not be a duplicate as the question implies that the user didn't know it is an async call — DSCH, Nov 19 '18 at 08:07

score 1 · Accepted Answer · answered Nov 18 '18 at 19:57

The issue is that userController.index() is an calling an async function. You should use a callback or a promise in order to fetch the data from you db. Promise example: Here we are returning a promise from the the executing the query on the Users collection.

const index = () => User.find({}).exec();

And in app.js:

case 'index-user':
        userController.index().then(result => {
          console.log(result); // as you use find there will be a list of user documents
        });
        break;

Or, you can use good old callbacks as so:

const index = (callback) => {
    User.find({}, function(err, res) {
        if (err) throw err;
        return callback(res);
    });
}

And in app.js:

case 'index-user':
        let indexUserResponse = userController.index((result) => {
          console.log(result); 
        });
        break;

When you execute it the way you do now, the console.log() runs before the index() method can execute the find() callback.

Hope it's clear enough and helps

This works just fine! Thanks a lot! – enbermudas Nov 18 '18 at 23:14 — enbermudas, Nov 18 '18 at 23:14

Console loggin a MongoDB collection. Undefined

1 Answers1