Mongoose doesn't yield findeOne results in co

Question

I'm using co and mongoose and I'd like to my asynchronous code look little more "synchronously" and - as far as I read - co library allows me use data from one yielded promise in another to avoid callback hell. It seems to work with mongoose save (even if I do multiple saves), but it does nothing with promises returned from queries like find() or findOne(). Why is that? What can I do to fix it?

Here'a a piece of my code:

co(function *() {
    let unhashedPassword = Math.random().toString(36);
    let passed = {
        username: 'T1',
        password: bcrypt.hashSync(unhashedPassword)
    };
    let saved = yield new test_model(passed).save();
    console.log("saved: " + saved);
    let found = yield test_model.findOne({username: saved.username}).exec();
    console.log("found" + found);
});

And the output:

saved: { _id: 57606dcf0f2378d41c355acd,
  password: '...',
  username: 'T1',
  __v: 0 }
Process finished with exit code 0

what if you just put `console.log("found");` ? does it reach that point ? seems weird you wouldn't even see the output from `console.log` — Willem D'Haeseleer, Jun 14 '16 at 21:13
Try catching errors [like here](http://stackoverflow.com/a/32215520/1048572). I'm quite sure you've got an exception. — Bergi, Jun 14 '16 at 21:16
@WillemD'Haeseleer, I did it after yieling test_model.findOne() and it's not printed - it doesn't reach that point. — Jarosław Rewers, Jun 14 '16 at 21:31
@Bergi - added the catch after co, even sorrounded findOne by try/catch and still nothing... — Jarosław Rewers, Jun 14 '16 at 21:31

Willem D'Haeseleer · Answer 1 · 2016-06-14T22:19:23.130

1

What do you see when you try this ?

co(function *() {
    let unhashedPassword = Math.random().toString(36);
    let passed = {
        username: 'T1',
        password: bcrypt.hashSync(unhashedPassword)
    };
    let saved = yield new test_model(passed).save();
    console.log('saved: ', saved);
    let foundPromise = test_model.findOne({username: saved.username}).exec()
    .then(function(value){
        console.log('fulfilled', value);
    }, function(error){
        console.log('error', error);
    });
    console.log('foundPromise', foundPromise);
    let found = yield foundPromise;
    console.log('found', found);
}).catch(function(error){
    console.log('catch', error);
});

edited Jun 14 '16 at 22:19

answered Jun 14 '16 at 21:55

Willem D'Haeseleer

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I removed the last yield (let found = yield foundPromise yield): saved: { _id: 57607fcf7cfca7980d37bc12, password: '$2a$10$Ebk6vFc5iai7yt7wTnT16e.0fOxEyvUE0jUqemYho44MfLUiACI0u', username: 'T1', __v: 0 } foundPromise Promise { emitter: EventEmitter { domain: null, _events: { reject: [Function] }, _eventsCount: 1, _maxListeners: undefined }, emitted: {}, ended: true } Process finished with exit code 0 – Jarosław Rewers Jun 14 '16 at 22:07

Mongoose doesn't yield findeOne results in co

1 Answers1