`timestamps` with `virtuals` break `toObject` return type

[skrukwa]

Prerequisites

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

Mongoose version

9.1.3

Node.js version

24.11.0

MongoDB server version

na

Typescript version (if applicable)

5.9.3

Description

It seems like using timestamps: true and defining virtuals on a schema causes some fields in the toObject type to incorrectly be {} | undefined.

When I remove timestamps: true OR remove the virtuals definition, the toObject types are correct.

Steps to Reproduce

import mongoose, { Schema } from 'mongoose';

const FooSchema = new Schema({
    foo: { type: String },
});

const PodcastSchema = new Schema({
    a: { type: FooSchema },
    b: { type: FooSchema, required: true },
    c: { type: String },
    d: { type: String, required: true },
}, {
    timestamps: true,
    virtuals: { hello: { get() { return 'hello world' } } },
});

const RootModel = mongoose.model('Root', PodcastSchema);

async function example() {
    const roots = await RootModel.find();
    const root = roots[0].toObject({ flattenMaps: true, flattenObjectIds: true, versionKey: false, virtuals: true });
    // const root: {
    //     id: string;
    //     a: {} | undefined;
    //     b: { ... 1 more } | null | undefined;
    //     c: {} | undefined;
    //     d: {} | undefined;
    //     hello: string;
    //     createdAt: NativeDate;
    //     updatedAt: NativeDate;
    // }
}

Expected Behavior

The toObject type should be:

const root: {
    id: string;
    a: { ... 1 more } | null | undefined;
    b: { ... 1 more };
    c: string | null | undefined;
    d: string;
    hello: string;
    createdAt: NativeDate;
    updatedAt: NativeDate;
}

[skrukwa]

@vkarpov15 can you reopen this issue (or instruct me to create a new issue)?

My project no longer builds with Mongoose 9.2 due to typescript errors. The toObject type has lost all of its fields.

    // Add to database
    const updatedPodcast = await PodcastModel.findByIdAndUpdate(
      podcastId,
      { $push: { documents: document } },
      { new: true }
    );
    if (!updatedPodcast || updatedPodcast.documents.length === 0) {
      throw new Error('Failed to add document to podcast');
    }
    const addedDoc = updatedPodcast.documents[updatedPodcast.documents.length - 1];

    const obj = addedDoc.toObject({ flattenObjectIds: true, versionKey: false, virtuals: true })

    // mongoose@9.1.6
    //
    // const obj: {
    //     [key: string]: any;
    //     title: string;
    //     type: string;
    //     text: string;
    //     source: DocumentSource.UPLOAD | DocumentSource.URL;
    //     originalFilename: string;
    //     cosUrl: string;
    //     addedAt: NativeDate;
    //     url: string | null | undefined;
    //     fileSize: number | null | undefined;
    // }

    // mongoose@9.2
    //
    // const obj: {
    //     [key: string]: any;
    // }

I presume it is related to this issue. Please let me know if you need more info to try and recreate the issue.

[vkarpov15]

@skrukwa can you please provide a more detailed repro script? I tried writing the following test and it seems to pass in Mongoose 9.2.

  const PodcastModel = mongoose.model('Test', new mongoose.Schema({
    title: String,
    type: String,
    text: String,
    documents: [new Schema({ answer: Number }, { _id: false })]
  }));
  const updatedPodcast = await PodcastModel.findByIdAndUpdate(
    '0'.repeat(24),
    { $push: { documents: { answer: 42 } } },
    { new: true }
  );
  if (!updatedPodcast || updatedPodcast.documents.length === 0) {
    throw new Error('Failed to add document to podcast');
  }
  const addedDoc = updatedPodcast.documents[updatedPodcast.documents.length - 1];

  const obj = addedDoc.toObject({ flattenObjectIds: true, versionKey: false, virtuals: true })
  ExpectType<{ answer?: number | null | undefined }>(obj);

[skrukwa]

it is fixed in 9.2.1