Document methods are not available when it is populated

[viganll]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.3.3

Node.js version

18.17.1

MongoDB server version

5

Typescript version (if applicable)

4.8

Description

After populating a field the document doesn't have the methods available. For instance, I have a user schema that has an instance method fullName. If I try to populate one of the fields of the user schema then typescript complains that the method fullName is not available.

This issue doesn't happen in 8.3.1.

Steps to Reproduce

import mongoose, { HydratedDocument, Model, Schema, Types, model } from "mongoose";

// Document definition
interface User {
  firstName: string;
  lastName: string;
  friend?: Types.ObjectId;
}

interface UserMethods {
  fullName(): string;
}

type UserModelType = Model<User, {}, UserMethods>;

const userSchema = new Schema<User, UserModelType, UserMethods>(
  {
    firstName: String,
    lastName: String,
    friend: { type: Schema.Types.ObjectId, ref: "User" },
  },
  {
    methods: {
      fullName() {
        return `${this.firstName} ${this.lastName}`;
      },
    },
  }
);
const userModel = model<User, UserModelType>("User", userSchema);

const UserModel = () => userModel;

async function run() {
  await mongoose.connect("mongodb://localhost:27017");
  await mongoose.connection.dropDatabase();

  const user1 = await UserModel().create({ firstName: "V", lastName: "B" });
  await UserModel().create({ firstName: "b", lastName: "B", friend: user1._id });

  const user = await UserModel().findOne({ firstName: "b" }).populate<{ friend: HydratedDocument<User, UserMethods> }>("friend").exec();
  if (!user) return;
  user.fullName(); // DOESN'T WORK -> Property 'fullName' does not exist on type
  user.friend?.fullName(); // works
}

run();

Expected Behavior

I would expect that there is no typescript errors and methods to be available even after populating a field.

[IslandRhythms]

const mongoose = require('mongoose');



const userSchema = new mongoose.Schema(
  {
    firstName: String,
    lastName: String,
    friend: { type: mongoose.Schema.Types.ObjectId, ref: "User" },
  },
  {
    methods: {
      fullName() {
        return `${this.firstName} ${this.lastName}`;
      },
    },
  }
);
const userModel = mongoose.model("User", userSchema);

const UserModel = () => userModel;

async function run() {
  await mongoose.connect("mongodb://localhost:27017");
  await mongoose.connection.dropDatabase();

  const user1 = await UserModel().create({ firstName: "V", lastName: "B" });
  await UserModel().create({ firstName: "b", lastName: "B", friend: user1._id });

  const user = await UserModel().findOne({ firstName: "b" }).populate("friend");
  if (!user) return;
  console.log('user.friend.fullName()', user.friend.fullName())
  console.log('user.fullName()', user.fulllName())
  user.fullName(); // DOESN'T WORK -> Property 'fullName' does not exist on type
  user.friend?.fullName(); // works
}

run();