Pushing a discriminated object in a non-discriminated array will strip its special properties

[anoirclere]

Hello,
I ran against this issue today.

I have these models :

var mongoose = require('mongoose'),
    Schema = mongoose.Schema;

var ThingContainerSchema = Schema({
  title: String,
  things: [{type: Schema.Types.ObjectId, ref: 'Thing'}]
});

module.exports = mongoose.model('ThingContainer', ThingContainerSchema);

var mongoose = require('mongoose'),
    Schema = mongoose.Schema,
    util = require('util');

// from https://github.com/LearnBoost/mongoose/pull/1647
function AbstractThingSchema() {
  Schema.apply(this, arguments);

  this.add({
    name: String,
  });
}
util.inherits(AbstractThingSchema, Schema);
module.exports = AbstractThingSchema;

var mongoose = require('mongoose'),
    AbstractThingSchema = require('./abstract_thing'),
    ThingSchema = new AbstractThingSchema();

module.exports = mongoose.model('Thing', ThingSchema);

var mongoose = require('mongoose'),
    Schema = mongoose.Schema,
    Thing = require('./thing'),
    AbstractThingSchema = require('./abstract_thing');

var SpecialThingSchema = new AbstractThingSchema({
  specialAttribute: String
});

module.exports = Thing.discriminator('SpecialThing', SpecialThingSchema);

Now, I have a ThingContainer and I want to add a SpecialThing to its array of Things. The issue is that the push method will cast the SpecialThing object and strip its "specialAttribute" as well as Mongoose's discriminating attribute "__t".

console.log(myThingContainer.things);
// [{_id: 544624d65a6efba21b558db3, name: "Thing 1"}, {_id: 544624d65a6efba21b558db4, name: "Thing 2"}]

var special = new SpecialThing({
  name: "Special Thing",
  specialAttribute: "Very Special"
});

console.log(special);
// {_id: 544625c8044511cd1bbfb28d, name: "Special Thing", __t: 'SpecialThing', specialAttribute: "Very Special"}


myThingContainer.things.push(special);
console.log(myThingContainer.things);
// [{_id: 544624d65a6efba21b558db3, name: "Thing 1"}, {_id: 544624d65a6efba21b558db4, name: "Thing 2"}, {_id: 544625c8044511cd1bbfb28d, name: "Special Thing"}]

My current workaround is to avoid the push method :

myThingContainer.things = myThingContainer.things.concat([special]);
console.log(myThingContainer.things);
// [{_id: 544624d65a6efba21b558db3, name: "Thing 1"}, {_id: 544624d65a6efba21b558db4, name: "Thing 2"}, {_id: 544625c8044511cd1bbfb28d, name: "Special Thing", __t: 'SpecialThing', specialAttribute: "Very Special"}]

I wonder if the push method should be aware of discriminated objects attributes ?

[vkarpov15]

Interesting. I'll take a look at this when I can.

[alabid]

@anoirclere myThingContainer.things already seems to have been populated. Can you provide a link to the entire project where you found this bug or just post some more code illustrating the bug? That'd be very helpful.

[anoirclere]

@alabid Yes in my case myThingContainer.things is populated. Do you mean push() is not supposed to work with populated arrays? Here's my code. A Building is a specialized Group, and a Residence contains an array of Group objects.

/*
 * Add building
 */
router.post('/', function(req, res, next) {
  var building = new Building({
    name: req.body.newBuildingName,
    type: req.body.newBuildingType,
    residence: req.residence._id,
  });

  building.save(function (err, building) {
    if(err) return next(err);

    //req.residence.groups.push(building);
    // The commented line above doesn't work since Mongoose will strip property '__t' from Building object at push.
    // Workaround : don't use rewritten "push" method.
    req.residence.groups = req.residence.groups.concat([building]);

    req.residence.groups.sort(function(a, b) {
      return (a.name < b.name) ? -1 : 1;
    });

    req.residence.save(function (err, residence) {
      if(err) return next(err);
      res.render('shared/_edit_buildings');
    });
  });
});