Node.js delayed promisify + mongoose

Question

Has anyone worked with nodejs 'offferred' and 'mongoose' modules? I am trying to get a deferred .promisify method to work on the functions of Mongolian models so that I can easily link them, but ran into some problems. In particular, I would like to promise the find and findById , so that I can chain to find one document referenced by another ObjectID document.

Here is what I have: https://gist.github.com/3321827

However, this seems less ideal as the getAppPermissions and getApplication seem a bit larger than the wrappers for the mongoose model's find and findById methods.

I tried just passing functions to promisify, but I get the error Object #<Object> has no method '_applyNamedScope' , which seems to be caused by the fact that this no longer bound to the correct object. Maybe I need to use underscore.bind? Has anyone been successful in this area, or should I just stick to what's working now?

Answer 1

Mariusz’s answer was pretty close. Here is what ultimately worked for me in this particular case, we hope others can learn from this:

 // I put this in my model file so I didn't have to worry about repeating it var userProto = mongoose.model('User'); userProto.pFind = deferred.promisify(userProto.find); userProto.pFindOne = deferred.promisify(userProto.findOne); 

Answer 2

You probably didn’t pass the context correctly to the methods, the right way to do this is to provide promising versions of the methods directly on the prototype of Mongoose:

 // I assume that methods you're using are set on mongoose.Model, // but be sure to check, maybe, they're using some other prototype (!) var promisify = require('deferred').promisify; var modelProto = mongoose.Model.prototype; modelProto.pFind = promisify(modelProto.find); modelProto.pFindById = promisify(modelProto.findById); // After that you may use promisified methods directly: app.get('/apps', requireLogin, function (req, res) { AppPermissions.pFind({ user: req.user.id, valid: true }) .map(function (permission) { return ApplicationRecord.pFindById(permission.application)( function (application) { application.permission = permisson; return application; } ); }).end(function (applications) { res.render('applist', { applications: applications }); }, null); }); 

You can also refrain from contaminating the prototype and use methods indirectly:

 var promisify = require('deferred').promisify; var modelProto = mongoose.Model.prototype; var pFind = promisify(modelProto.find); var pFindById = promisify(modelProto.findById); app.get('/apps', requireLogin, function (req, res) { pFind.call(AppPermissions, { user: req.user.id, valid: true }) .map(function (permission) { return pFindById.call(ApplicationRecord, permission.application)( function (application) { application.permission = permisson; return application; } ); }).end(function (applications) { res.render('applist', { applications: applications }); }, null); });