flattenObjectIds toObject option side effects

[stevemit007]

Prerequisites

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

Mongoose version

7.4.0

Node.js version

16.17.0

MongoDB server version

6.0.3

Typescript version (if applicable)

5.1.6

Description

Creating a schema with option

toObject: {
  flattenObjectIds: true
}

has unwanted side effects.

MongoDB Compass shows the autogenerated _id field has type string, and Model.findById() returns null.

A workaround is to use toJSON() instead of toObject().

Steps to Reproduce

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

interface IUser {
  name: string;
}
const UserSchema = new Schema<IUser>(
  {
    name: String
  },
  {
    toObject: { flattenObjectIds: true }
  }
);
const User: Model<IUser> = model("User", UserSchema);
User.create({ name: "George" }).then((d) => {
  User.findById(d._id)
    .exec()
    .then((d) => console.log(d));
});

Expected Behavior

Result is not null.

[IslandRhythms]

import { Model, Schema, model, connect, connection } from "mongoose";

interface IUser {
  name: string;
}
const UserSchema = new Schema<IUser>(
  {
    name: String
  },
  {
    toObject: { flattenObjectIds: true }
  }
);
const User: Model<IUser> = model("User", UserSchema);
async function run() {
  await connect('mongodb://localhost:27017');
  await connection.dropDatabase();
  User.create({ name: "George" }).then((d) => {
    User.findById(d._id)
      .exec()
      .then((d) => console.log(d));
  });
}

run();