Discriminators cause fields in subdocuments to be deselected by default

[walterrw]

Using discriminators on subdocument schema causes fields to be deselected in query.

var itemSchema = new Schema({ 
  type: String, 
  active: { type: Boolean, default: true }
}, {
  discriminatorKey: 'type'
});

var collectionSchema = new Schema({ 
  items: [itemSchema] 
});

collectionSchema.path('items').discriminator('type1', new Schema({ count: Number }));

var collection = mongoose.model('Collection', collectionSchema);
collection.create({ 
  items: [ 
    { type: 'type1', active: false, count: 3 }
  ]
});

If I execute the query

collection.find().select('items');

I'd expect the result to be { :items [{ type: 'type1', active: false, count: 3 }]}.
Instead, it returns {:items [{ type: 'type1' }]}.

When I don't specify any fields for the query it behaves as expected.

---

mongoDB version: 3.4.1
node version: 8.5.0
mongoose version: 4.12.5

[vkarpov15]

Thanks for reporting, will investigate ASAP

[sobafuchs]

yup, that does seem to be happening:

const mongoose = require('mongoose');
const co = require('co');
mongoose.Promise = global.Promise;
const GITHUB_ISSUE = `gh-5775`;

const { Schema } = mongoose;

exec()
  .then(() => {
    console.log('successfully ran program');
    process.exit(0);
  })
  .catch(error => {
    console.error(`Error: ${error}\n${error.stack}`);
  });


function exec() {
  return co(function* () {
    yield mongoose.connect(`mongodb://localhost:27017/${GITHUB_ISSUE}`, { useMongoClient: true });
    var itemSchema = new Schema({
      type: String,
      active: { type: Boolean, default: true }
    }, {
        discriminatorKey: 'type'
      });

    var collectionSchema = new Schema({
      items: [itemSchema]
    });

    collectionSchema.path('items').discriminator('type1', new Schema({ count: Number }));

    var collection = mongoose.model('Collection', collectionSchema);
    yield collection.create({
      items: [
        { type: 'type1', active: false, count: 3 }
      ]
    });

    console.log((yield collection.find().select('items'))[0].items);
  });
}

I wonder if this has something to do with you using type as a field on the schema

[walterrw]

It happens also if I use the default discriminatorKey