Discriminators causing everything to be "unselected" when using "select"

[wlingke]

I am attempting to use .select in a query with a discriminator model. The example below uses the projection to pull a textScore (meant for use with a $text query) but the bug is not specifically related to this use case.

When making a find call, the returned objects do NOT have trackField or eventField and they are selected out automatically without me specifying it.

See Repro Script:

const mongoose = require('./');
mongoose.set('debug', true);

const Schema = mongoose.Schema;

mongoose.connect('mongodb://127.0.0.1/test');
const db = mongoose.connection;

db.once('open', async () => {
  try {
    const eventSchema = new Schema({
      eventField: String
    }, { id: false });

    const Event = mongoose.model('Event', eventSchema);

    const trackSchema = new Schema({
      trackField: String,
    });

    const Track = Event.discriminator('Track', trackSchema);

    const trackedItem = new Track({
      trackField: 'trackField',
      eventField: 'eventField',
    });
    await trackedItem.save();

    const events = await Event.find({}).select({ score: { $meta: 'textScore' } }).exec();
    const tracks = await Track.find({}).select({ score: { $meta: 'textScore' } }).exec();
    console.log(events); // no trackField or eventField
    console.log(tracks); // no trackField or eventField

    db.close();
  } catch (e) {
    console.log(e);
  }
});

When you attach the debugger, it shows this query:
events.find({}, { fields: { score: { '$meta': 'textScore' }, __t: 1 } })

I imagine that the __t: 1 is causing this.

If I run await Event.find({}).exec(), the mongoose debugger shows
events.find({}, { fields: {} }) which is why normally everything is selected.

The problem that this causes is that you can't run a $text query sorting by textScore on anything that has a discriminator without specifically projecting every single field in the schema.

Is there any way to override the __t: 1? I tried setting {__t: null} but that didn't work. Or is there a mongodb projection operator that I'm not aware that might solve this problem?

[vkarpov15]

Thanks for the detailed repro, will fix. The __t: 1 getting added is a bug, mongoose should only add it if the user-provided projection is inclusive. { score: { $meta: 'textScore' } } is not an inclusive projection, so I imagine we're checking for truthiness somewhere as opposed to looking for $meta and $slice.

[wlingke]

awesome thanks so much

[dimaip]

The __t: 1 getting added is a bug

Is it a different bug then? I have the same problem, I have a BaseUser model and User model discriminated on top of it.
When I do query like this BaseUser.findById(req.user._id, '+email') I'm only getting the email field in response. This happens because __t gets included in the query, and so it yields exclude = false in applyPaths.

This problem happens on mongoos 4.13.18, on 5.x it seems to work correctly.

[vkarpov15]

@dimaip looks like this bug was fixed in 5.x then. Is there something that prevents you from upgrading?

[dimaip]

@vkarpov15 I already did, the upgrade process went smooth.