find on ObjectIds not working after insertMany

[DrChrispoper]

Prerequisites

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

Mongoose version

8.7.0

Node.js version

18.x

MongoDB server version

7.0.12

Typescript version (if applicable)

^5.1.6

Description

After insertMany calling find with on an ObjectId parameter, it will fail to return any rows.

The issue happens when I have both a property of type: [Schema.Types.Mixed] and toObject: { flattenObjectIds: true }
I'm not sure why, but I've done written a jest test to show.

Steps to Reproduce

import db from '../helper/mockDb'
import mongoose, { Schema, Types } from 'mongoose'

const userId = new Types.ObjectId()

beforeAll(async () => {
  await db.connect()
})

afterAll(async () => {
  await db.disconnect()
})

describe('Basic insertMany test', () => {
  const TestSchema = new Schema(
    {
      professionalId: {
        type: Schema.Types.ObjectId,
      },
      firstName: {
        type: String,
      },
    },
    {
      toObject: { flattenObjectIds: true },
    },
  )

  const TestModel = mongoose.model('testSchema', TestSchema)

  const SimpleExternalClientSchema = new Schema(
    {
      professionalId: {
        type: Schema.Types.ObjectId,
      },
      firstName: {
        type: String,
        default: '',
        required: true,
        trim: true,
      },
      addresses: {
        type: [Schema.Types.Mixed],
        default: [],
      },
    },
    {
      toObject: { flattenObjectIds: true },
    },
  )

  const SimpleExternalClientModel = mongoose.model('simpleExternalClient', SimpleExternalClientSchema)

  test('Should insert multiple records', async () => {
    const data = [
      { professionalId: userId, firstName: 'Testy' },
      { professionalId: userId, firstName: 'Johny' },
    ]

    await TestModel.insertMany(data)

    const records = await TestModel.find({}).exec()
    expect(records.length).toEqual(2)

    const recordFiltered = await TestModel.find({ professionalId: userId }).exec()
    expect(recordFiltered.length).toEqual(2) // <- This works
  })

  test('Should insert client multiple records', async () => {
    const externalClientData = [{
      firstName: 'Testy',
      professionalId: userId,
    }, {
      firstName: 'Testy',
      professionalId: userId,
    }]

    await SimpleExternalClientModel.insertMany(externalClientData)

    const records = await SimpleExternalClientModel.find({}).exec()
    expect(records.length).toEqual(2)

    const recordFiltered = await SimpleExternalClientModel.find({ professionalId: userId }).exec()
    expect(recordFiltered.length).toEqual(2) // <-- This is the line that is failing
  })
})

Expected Behavior

Second test should pass

[vkarpov15]

We have a fix in #14938 and will ship that fix in our next patch release.

As a workaround, you can:

1. set flattenObjectIds to false in your schema
2. use create() instead of insertMany()

[DrChrispoper]

Thanks for the help and the quick response. 🙏