mongoose + promises experiments - https://github.com/yamadapc/mongoose-bluebird-utils/issues/1

mongoose-experiments.js

'use strict';
var mongoose = require('mongoose'),
    Promise  = require('bluebird');

mongoose.connect('mongodb://localhost/test');

var SomethingSchema = new mongoose.Schema({
  name: String
});

SomethingSchema.pre('save', function(next) {
  this.name = 'something';
  next();
});
var Something = mongoose.model('Something', SomethingSchema);

Promise.promisifyAll(mongoose.Model);
Promise.promisifyAll(mongoose.Model.prototype);

/**
 * Using saveAsync
 * --------------------------------------------------------------------------*/

var somethingAsync = new Something({ name: 'asdf' });
somethingAsync.saveAsync()
  .spread(function(something) {
    console.log('Using `saveAsync` =>', something.name); // asdf
  });

/**
 * Using save
 * --------------------------------------------------------------------------*/

var something = new Something({ name: 'asdf' });
something.save(function(err, something) {
  console.log('Using `save` =>', something.name); // something
});

/**
 * Using Something.prototype.save.call
 * --------------------------------------------------------------------------*/

var somethingWeird = new Something({ name: 'asdf' });
Something.prototype.save.call(somethingWeird, function(err, something) {
  console.log('Using `Something.prototype.save.call` =>', something.name); // => asdf
});

/**
 * Using something.save.call
 * --------------------------------------------------------------------------*/

var somethingWeirder = new Something({ name: 'asdf '});
something.save.call(somethingWeirder, function(err, something) {
  console.log('something.save.call =>', something.name); // => something
});