find failures when using promises

[Mark Edwards]

tearing my hair out here... fortunately I still have a few follicles left.

I have an app that requires some update operations to be sequential, so I am using the promise API's to attempt to achieve this.

Unfortunately, I'm experiencing some query failures where using the .exec() suffix simply results in the results array becoming undefined.

When I run this query outside of the promise structure, I'm seeing results, but not when it's within the promise structure.

I am constrained to using the promise structure to avoid race conditions.

This is my methodology in the code...

var pFreqDeliver=goose.frequency                              
.find({'block':data.block})
.exec(function(e,a) {
 console.log('inside pFreqDeliver...');
  console.log(a);
  var resp={'block':data.block,'content':a};
  socket.emit("rxfrequpdate",resp)
});

var pDoIt=pTalent.then(function(){console.log('pTalent Done');})
                                .chain(pOutput)
                                .then(function(){console.log('pOutput Done');})
                                .chain(pFreq)
                                .then(function(){console.log('pFreq Done');})
                                .chain(pFreqUpdate)
                                .then(function(){console.log('pFreqUpdate Done');})
                                .chain(pCommit)
                                .then(function(){console.log('pCommit Done');})
                                .chain(pFreqDeliver)
                                .then(function(freqs){
                                        console.log(freqs);
                                        console.log('pFreqDeliver Done');
                                });
pDoIt.fulfill();

I have only shown the problematic promise... pFreqDeliver.

Whereas there is heaps of data in this collection - the console log shows undefined upon return.

If I change this to a find(<conditions>,<callback>) pattern, I can see data, but the promise structure breaks.

Any ideas?

Thanks in advance...

Mark...

[Jason Crawford]

I really don't know, but a year or two ago I had a different problem with Mongoose promises (they weren't playing nicely with chai-as-promised: https://github.com/domenic/chai-as-promised/issues/30), and so I started using Q promises instead, like this:

var Q = require('q');

mongoose.Query.prototype.qexec = function () {

  return Q.npost(this, 'exec', arguments);

}

Now I use qexec() instead of exec() and everything works well. You could try that and see if it helps.

Good luck,

Jason

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[Mark Edwards]

Jason, thanks for this. Yeah googling around about goose and promises did mention a few posts about "q". You'll have to forgive - I'm very much a newbie who has simply jumped into the deep end of async paradigms, node js, mongo and goose - still very much learning the ropes. Promises could be a saviour to ensure everything happens in the right order, just gotta get the right model to work!

Cheers mate.

m

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regards,

Mark P. Edwards

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[Jason Crawford]

No need to apologize! I've had a good experience overall with promises, see what I wrote here: https://www.quora.com/Should-I-learn-and-use-the-promise-pattern-in-JavaScript/answer/Jason-Crawford

But not all promise implementations behave exactly the same way, and the ones built into Mongoose weren't working with chai-as-promised, so maybe there's something a little odd about them.

Best of luck,

Jason