Embedded discriminators with "tiedValue" dont populate without explicitly specifing "model"

[hasezoey]

Do you want to request a feature or report a bug?
bug

What is the current behavior?
When using Embedded discriminators with tiedValue instead of just name it doesn't populate without also specifying model on populate call

If the current behavior is a bug, please provide the steps to reproduce.

// NodeJS: 16.1.0
// MongoDB: 4.2-bionic (Docker)
import * as mongoose from "mongoose"; // mongoose@5.12.7
import { inspect } from "util";
import { schemas } from "@typegoose/typegoose/lib/internal/data";

enum ActivityKind {
  Talk = "TALK",
  None = "NONE"
}

const GuestSchema = new mongoose.Schema({
  dummy: String
});

const ActivitySchema = new mongoose.Schema({
  title: String,
  kind: { required: true, type: String, enum: [ActivityKind.Talk] }
}, { discriminatorKey: "kind" });

const ActivityTalkSchema = new mongoose.Schema({
  speakers: [{ type: mongoose.Schema.Types.ObjectId, ref: "Guest" }]
});
ActivityTalkSchema.add(ActivitySchema);
// skip check because otherwise "add" can not be used
(ActivityTalkSchema.paths.kind as any).options.$skipDiscriminatorCheck = true;

const SponsorSchema = new mongoose.Schema({
  speakers: [{ type: mongoose.Schema.Types.ObjectId, ref: "Guest" }]
});

const ProgrammeSchema = new mongoose.Schema({
  sponsors: [SponsorSchema],
  activities: [{
    required: true,
    type: ActivitySchema
  }]
});
// @ts-expect-error mongoose does not have typings for "discriminator" without casting beforehand to DocumentArray
ProgrammeSchema.path("activities").discriminator("ActivityTalk", ActivityTalkSchema, ActivityKind.Talk);

const GuestModel = mongoose.model("Guest", GuestSchema);
const ProgrammeModel = mongoose.model("Programme", ProgrammeSchema);

(async () => {
  console.log(inspect(schemas.get("Activity"), false, 5));
  await mongoose.connect(`mongodb://localhost:27017/`, { useNewUrlParser: true, dbName: "verifyMASTER", useCreateIndex: true, useUnifiedTopology: true });

  // seed the database
  const guest1 = await GuestModel.create({ dummy: "1" });
  const guest2 = await GuestModel.create({ dummy: "2" });

  const programme1 = await ProgrammeModel.create({
    sponsors: [
      { speakers: [guest1, guest2] }
    ],
    activities: [
      { title: "hello", kind: ActivityKind.Talk, speakers: [guest1, guest2] }
    ]
  });

  const event = await ProgrammeModel.findOne({ _id: programme1._id }).orFail().exec();
  console.log("found", inspect(event, false, 5, true));
  await event.populate({ path: "activities.speakers" }).execPopulate();

  console.log("populate", inspect(event, false, 5, true));

  await mongoose.disconnect();
})();

{
    "compileOnSave": true,
    "typeAcquisition": {
        "enable": true
    },
    "compilerOptions": {
        "experimentalDecorators": true,
        "emitDecoratorMetadata": true,
        "declarationMap": true,
        "outDir": "lib",
        "moduleResolution": "node",
        "target": "es6",
        "module": "commonjs",
        "newLine": "LF",
        "sourceMap": true,
        "removeComments": true,
        "strict": true,
        "allowUnreachableCode": false,
        "pretty": true,
        "declaration": true,
        "incremental": true,
        "tsBuildInfoFile": ".tsbuildinfo",
        "lib": [
            "esnext"
        ]
    },
    "include": [
        "src/**/*"
    ]
}

What is the expected behavior?
to populate without also specifying model

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
nodejs: 16.1.0
mongoose: 5.12.7
typescript: 4.2.4

PS: documentation taken from here

Note: populate work when not using tiedValue

PPS: if needed, there is also an reproduction repository with this code: https://github.com/typegoose/typegoose-testing/tree/verify537

[hasezoey]

just wanna add:
this example is made with typescript, but should not be necessary to reproduce this issue - it is just for convenience

[IslandRhythms]

const mongoose = require('mongoose');
const util = require('util');
const {inspect} = util;
const {Schema} = mongoose;

const GuestSchema = new Schema ({
    dummy: String
});

const ActivitySchema = new Schema({
    title: String,
    kind: {required: true, type: String, enum: ["TALK"]}}, 
    {discriminatorKey: "kind"})

const ActivityTalkSchema = new Schema({
    speakers: [{type: mongoose.Schema.Types.ObjectId, ref: "Guest"}]
});

ActivityTalkSchema.add(ActivitySchema);

ActivityTalkSchema.paths.kind.options.$skipDiscriminatorCheck = true;

const SponsorSchema = new Schema({
    speakers: [{type: mongoose.Schema.Types.ObjectId, ref: "Guest"}]
});

const ProgrammeSchema = new Schema({
    sponsors: [SponsorSchema],
    activities: [{required: true, type: ActivitySchema}]
});

ProgrammeSchema.path("activities").discriminator("ActivityTalk", ActivityTalkSchema, "TALK");

const GuestModel = mongoose.model("Guest", GuestSchema);
const ProgrammeModel = mongoose.model("Programmer", ProgrammeSchema);

async function test() {
await mongoose.connect('mongodb://localhost:27017/', {
    useNewUrlParser: true,
    useCreateIndex: true,
    useUnifiedTopology: true
});

const guest1 = await GuestModel.create({dummy: "1"})
const guest2 = await GuestModel.create({dummy: "2"});

const programme1 = await ProgrammeModel.create({sponsors: [
    {speakers: [guest1, guest2]}
],
activities: [
    {title: "hello", kind: "TALK"}
]});

const event = await ProgrammeModel.findOne({_id: programme1._id}).orFail().exec();
console.log("found", inspect(event, false, 5, true));
await event.populate({path: "activities.speakers"}).execPopulate();
console.log("populate", inspect(event, false, 5, true));
await mongoose.disconnect();
}

test();

Output:

found {
  _id: 609c39bef31ef11ddcead82f,
  sponsors: [
    {
      speakers: [ 609c39bef31ef11ddcead82d, 609c39bef31ef11ddcead82e ],
      _id: 609c39bef31ef11ddcead830
    }
  ],
  activities: [
    {
      speakers: [],
      kind: 'TALK',
      _id: 609c39bef31ef11ddcead831,
      title: 'hello'
    }
  ],
  __v: 0
}
populate {
  _id: 609c39bef31ef11ddcead82f,
  sponsors: [
    {
      speakers: [ 609c39bef31ef11ddcead82d, 609c39bef31ef11ddcead82e ],
      _id: 609c39bef31ef11ddcead830
    }
  ],
  activities: [
    {
      speakers: [],
      kind: 'TALK',
      _id: 609c39bef31ef11ddcead831,
      title: 'hello'
    }
  ],
  __v: 0
}

[hasezoey]

@IslandRhythms what exactly "needs clarification"?

[vkarpov15]

@hasezoey "needs clarification" means we don't think we have enough info to reasonably try to repro this issue.

[hasezoey]

@vkarpov15 i basically know what i means, i just asked what was needed aside from the information already given (i mean versions are there, problem is stated and reproduction script is also provided (and confirmed to reproduce at the time?))